25723423515

Committed 12 May 2026 08:40AM UTC coverage: 87.644% (+0.03%) from 87.619%

Build # 25723423515

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github

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web-flow

Commit Message

Fix: Use generic errors in the variable mapper and expr. (#16132)

While in the past we relied on `PyResult` to handle all of the errors as python exceptions, we can now remove some of the dependencies in parts of our system.
After some evaluation, it turns out we can use generic errors in the `VariableMapper` and `Expr` which frees us from needing python in order to use these components.

This was discovered during efforts to separate `DAGCircuit`'s error messages from always using `PyErr`.

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4 existing lines in 3 files now uncovered.

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91.04

/crates/circuit/src/parameter/parameter_expression.rs

// This code is part of Qiskit.
//
// (C) Copyright IBM 2023, 2024
//
// This code is licensed under the Apache License, Version 2.0. You may
// obtain a copy of this license in the LICENSE.txt file in the root directory
// of this source tree or at https://www.apache.org/licenses/LICENSE-2.0.
//
// Any modifications or derivative works of this code must retain this
// copyright notice, and modified files need to carry a notice indicating
// that they have been altered from the originals.

use hashbrown::hash_map::Entry;
use hashbrown::{HashMap, HashSet};
use indexmap::IndexSet;
use num_complex::Complex64;
use pyo3::exceptions::{PyRuntimeError, PyTypeError, PyValueError, PyZeroDivisionError};
use pyo3::types::{IntoPyDict, PyComplex, PyFloat, PyInt, PyNotImplemented, PySet, PyString};
use std::sync::Arc;
use thiserror::Error;
use uuid::Uuid;

use std::collections::hash_map::DefaultHasher;
use std::fmt;
use std::hash::{Hash, Hasher};

use pyo3::IntoPyObjectExt;
use pyo3::prelude::*;

use crate::circuit_data::CircuitError;
use crate::imports::{BUILTIN_HASH, SYMPIFY_PARAMETER_EXPRESSION, UUID};
use crate::parameter::symbol_expr;
use crate::parameter::symbol_expr::SymbolExpr;
use crate::parameter::symbol_parser::parse_expression;

use super::symbol_expr::{SYMEXPR_EPSILON, Symbol, Value};

/// Errors for dealing with parameters and parameter expressions.
#[derive(Error, Debug)]
pub enum ParameterError {
    #[error("Division by zero.")]
    ZeroDivisionError,
    #[error("Binding to infinite value.")]
    BindingInf,
    #[error("Binding to NaN.")]
    BindingNaN,
    #[error("Invalid value: NaN or infinite.")]
    InvalidValue,
    #[error("Cannot bind following parameters not present in expression: {0:?}")]
    UnknownParameters(HashSet<Symbol>),
    #[error("Parameter expression with unbound parameters {0:?} is not numeric.")]
    UnboundParameters(HashSet<Symbol>),
    #[error("Name conflict adding parameters.")]
    NameConflict,
    #[error("Invalid cast to OpCode: {0}")]
    InvalidU8ToOpCode(u8),
    #[error("Could not cast to Symbol.")]
    NotASymbol,
    #[error("Derivative not supported on expression: {0}")]
    DerivativeNotSupported(String),
}

impl From<ParameterError> for PyErr {
    fn from(value: ParameterError) -> Self {
        match value {
            ParameterError::ZeroDivisionError => {
                PyZeroDivisionError::new_err("zero division occurs while binding parameter")
            }
            ParameterError::BindingInf => {
                PyZeroDivisionError::new_err("attempted to bind infinite value to parameter")
            }
            ParameterError::UnknownParameters(_) | ParameterError::NameConflict => {
                CircuitError::new_err(value.to_string())
            }
            ParameterError::UnboundParameters(_) => PyTypeError::new_err(value.to_string()),
            ParameterError::InvalidValue => PyValueError::new_err(value.to_string()),
            _ => PyRuntimeError::new_err(value.to_string()),
        }
    }
}

/// A parameter expression.
///
/// This is backed by Qiskit's symbolic expression engine and a cache
/// for the parameters inside the expression.
#[derive(Clone, Debug)]
pub struct ParameterExpression {
    // The symbolic expression.
    expr: SymbolExpr,
    // A map keeping track of all symbols, with their name. This map *must* have
    // exactly one entry per symbol used in the expression (no more, no less).
    name_map: HashMap<String, Symbol>,
}

impl Hash for ParameterExpression {
    fn hash<H: Hasher>(&self, state: &mut H) {
        // The string representation of a tree is unique.
        self.expr.string_id().hash(state);
    }
}

impl PartialEq for ParameterExpression {
    fn eq(&self, other: &Self) -> bool {
        self.expr.eq(&other.expr)
    }
}

impl Eq for ParameterExpression {}

impl Default for ParameterExpression {
    /// The default constructor returns zero.
    fn default() -> Self {
        Self {
            expr: SymbolExpr::Value(Value::Int(0)),
            name_map: HashMap::new(), // no parameters, hence empty name map
        }
    }
}

impl fmt::Display for ParameterExpression {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(f, "{}", {
            if let SymbolExpr::Symbol(s) = &self.expr {
                s.repr(false)
            } else {
                match self.expr.eval(true) {
                    Some(e) => e.to_string(),
                    None => self.expr.to_string(),
                }
            }
        })
    }
}

impl ParameterExpression {
    pub fn qpy_replay(&self) -> Vec<OPReplay> {
        let mut replay = Vec::new();
        let mut unused: IndexSet<_, foldhash::fast::RandomState> =
            self.name_map.values().cloned().collect();
        // The recursive inner `qpy_replay_inner` assumes it starts from a containing operation, so
        // fails to build a complete replay in the case it starts from a single symbol or value.
        match &self.expr {
            SymbolExpr::Value(v) => {
                let item = match *v {
                    Value::Int(v) => OPReplay {
                        op: OpCode::ADD,
                        lhs: Some(ParameterValueType::Int(v)),
                        rhs: Some(ParameterValueType::Int(0)),
                    },
                    Value::Real(v) => OPReplay {
                        op: OpCode::ADD,
                        lhs: Some(ParameterValueType::Float(v)),
                        // `-0.0` is technically the identity element of floating-point addition;
                        // `0.0 + x` is not bit-for-bit equal to `x` solely if `x` is `-0.0`.
                        rhs: Some(ParameterValueType::Float(-0.0)),
                    },
                    Value::Complex(v) => OPReplay {
                        op: OpCode::ADD,
                        lhs: Some(ParameterValueType::Complex(v)),
                        rhs: Some(ParameterValueType::Complex(Complex64 {
                            re: -0.0,
                            im: -0.0,
                        })),
                    },
                };
                replay.push(item);
            }
            SymbolExpr::Symbol(sym) => {
                unused.swap_remove(sym.as_ref());
                replay.push(OPReplay {
                    op: OpCode::ADD,
                    lhs: ParameterValueType::extract_from_expr(&self.expr),
                    rhs: Some(ParameterValueType::Int(0)),
                });
            }
            SymbolExpr::Unary { .. } | SymbolExpr::Binary { .. } => {
                qpy_replay_inner(self, &self.name_map, &mut replay, &mut unused);
            }
        }
        // For any unused symbols, we'll add something like `(x * 0) + expr`.  This sort of
        // cancellation is how unused symbols appear; it doesn't matter if the _actual_ cause was
        // `x - x` or whatever, because the end observable effect is the same.
        for symbol in unused {
            replay.push(OPReplay {
                op: OpCode::MUL,
                lhs: Some(ParameterValueType::from_symbol(symbol)),
                rhs: Some(ParameterValueType::Int(0)),
            });
            replay.push(OPReplay {
                op: OpCode::ADD,
                lhs: None,
                rhs: None,
            });
        }
        replay
    }
}
// This needs to be implemented manually, because PyO3 does not provide built-in
// conversions for the subclasses of ParameterExpression in Python. Specifically
// the Python classes Parameter and ParameterVector are subclasses of
// ParameterExpression and the default trait impl would not handle the specialization
// there.
impl<'py> IntoPyObject<'py> for ParameterExpression {
    type Target = PyParameterExpression;
    type Output = Bound<'py, Self::Target>;
    type Error = PyErr;

    fn into_pyobject(self, py: Python<'py>) -> Result<Self::Output, Self::Error> {
        let expr = PyParameterExpression::from(self.clone());
        expr.into_pyobject(py)
    }
}

/// Lookup for which operations are binary (i.e. require two operands).
static BINARY_OPS: [OpCode; 8] = [
    // a HashSet would be better but requires unstable features
    OpCode::ADD,
    OpCode::SUB,
    OpCode::MUL,
    OpCode::DIV,
    OpCode::POW,
    OpCode::RSUB,
    OpCode::RDIV,
    OpCode::RPOW,
];

impl ParameterExpression {
    /// Initialize with an existing [SymbolExpr] and its valid name map.
    ///
    /// Caution: The caller **guarantees** that ``name_map`` is consistent with ``expr``.
    /// If uncertain, call [Self::from_symbol_expr], which automatically builds the correct name map.
    pub fn new(expr: SymbolExpr, name_map: HashMap<String, Symbol>) -> Self {
        Self { expr, name_map }
    }

    /// Construct from a [Symbol].
    pub fn from_symbol(symbol: Symbol) -> Self {
        Self {
            expr: SymbolExpr::Symbol(Arc::new(symbol.clone())),
            name_map: [(symbol.repr(false), symbol)].into(),
        }
    }

    /// Try casting to a [Symbol].
    ///
    /// This only succeeds if the underlying expression is, in fact, only a symbol.
    pub fn try_to_symbol(&self) -> Result<Symbol, ParameterError> {
        self.try_to_symbol_ref().cloned()
    }

    /// Try casting to a [Symbol], returning a reference.
    ///
    /// This only succeeds if the underlying expression is, in fact, only a symbol.
    pub fn try_to_symbol_ref(&self) -> Result<&Symbol, ParameterError> {
        match &self.expr {
            SymbolExpr::Symbol(sym) if self.name_map.len() == 1 => Ok(sym.as_ref()),
            _ => Err(ParameterError::NotASymbol),
        }
    }

    /// Try casting to a [Value].
    ///
    /// Attempt to evaluate the expression recursively and return a [Value] if fully bound.
    ///
    /// # Arguments
    ///
    /// * strict - If ``true``, only allow returning a value if all symbols are bound. If
    ///   ``false``, allow casting expressions to values, even though symbols might still exist.
    ///   For example, ``0 * x`` will return ``0`` for ``strict=false`` and otherwise return
    ///   an error.
    pub fn try_to_value(&self, strict: bool) -> Result<Value, ParameterError> {
        if strict && !self.name_map.is_empty() {
            let free_symbols = self.expr.iter_symbols().cloned().collect();
            return Err(ParameterError::UnboundParameters(free_symbols));
        }

        match self.expr.eval(true) {
            Some(value) => {
                // we try to restrict complex to real, if possible
                if let Value::Complex(c) = value {
                    if (-symbol_expr::SYMEXPR_EPSILON..symbol_expr::SYMEXPR_EPSILON).contains(&c.im)
                    {
                        return Ok(Value::Real(c.re));
                    }
                }
                Ok(value)
            }
            None => {
                let free_symbols = self.expr.iter_symbols().cloned().collect();
                Err(ParameterError::UnboundParameters(free_symbols))
            }
        }
    }

    /// Construct from a [SymbolExpr].
    ///
    /// This populates the name map with the symbols in the expression.
    pub fn from_symbol_expr(expr: SymbolExpr) -> Self {
        let name_map = expr.name_map();
        Self { expr, name_map }
    }

    /// Initialize from an f64.
    pub fn from_f64(value: f64) -> Self {
        Self {
            expr: SymbolExpr::Value(Value::Real(value)),
            name_map: HashMap::new(),
        }
    }

    /// Load from a sequence of [OPReplay]s. Used in serialization.
    pub fn from_qpy(replay: &[OPReplay]) -> Result<Self, ParameterError> {
        // the stack contains the latest lhs and rhs values
        let mut stack: Vec<ParameterExpression> = Vec::new();
        for OPReplay { op, lhs, rhs } in replay {
            // put the values on the stack, if they exist
            if let Some(value) = lhs {
                stack.push(value.clone().into());
            }
            if let Some(value) = rhs {
                stack.push(value.clone().into());
            }

            // if we need two operands, pop rhs from the stack
            let rhs = if BINARY_OPS.contains(op) {
                Some(stack.pop().expect("Pop from empty stack"))
            } else {
                None
            };

            // pop lhs from the stack, this we always need
            let lhs = stack.pop().expect("Pop from empty stack");

            // apply the operation and put the result onto the stack for the next replay
            let result: ParameterExpression = match op {
                OpCode::ADD => lhs.add(&rhs.unwrap())?,
                OpCode::MUL => lhs.mul(&rhs.unwrap())?,
                OpCode::SUB => lhs.sub(&rhs.unwrap())?,
                OpCode::RSUB => rhs.unwrap().sub(&lhs)?,
                OpCode::POW => lhs.pow(&rhs.unwrap())?,
                OpCode::RPOW => rhs.unwrap().pow(&lhs)?,
                OpCode::DIV => lhs.div(&rhs.unwrap())?,
                OpCode::RDIV => rhs.unwrap().div(&lhs)?,
                OpCode::ABS => lhs.abs(),
                OpCode::SIN => lhs.sin(),
                OpCode::ASIN => lhs.asin(),
                OpCode::COS => lhs.cos(),
                OpCode::ACOS => lhs.acos(),
                OpCode::TAN => lhs.tan(),
                OpCode::ATAN => lhs.atan(),
                OpCode::CONJ => lhs.conjugate(),
                OpCode::LOG => lhs.log(),
                OpCode::EXP => lhs.exp(),
                OpCode::SIGN => lhs.sign(),
                OpCode::GRAD | OpCode::SUBSTITUTE => {
                    panic!("GRAD and SUBSTITUTE are not supported.")
                }
            };
            stack.push(result);
        }

        // once we're done, just return the last element in the stack
        Ok(stack
            .pop()
            .expect("Invalid QPY replay encountered during deserialization: empty OPReplay."))
    }

    pub fn iter_symbols(&self) -> impl Iterator<Item = &Symbol> + '_ {
        self.name_map.values()
    }

    /// Get the number of [Symbol]s in the expression.
    pub fn num_symbols(&self) -> usize {
        self.name_map.len()
    }

    /// Whether the expression represents a complex number. None if cannot be determined.
    pub fn is_complex(&self) -> Option<bool> {
        self.expr.is_complex()
    }

    /// Whether the expression represents a int. None if cannot be determined.
    pub fn is_int(&self) -> Option<bool> {
        self.expr.is_int()
    }

    /// Add an expression; ``self + rhs``.
    pub fn add(&self, rhs: &ParameterExpression) -> Result<Self, ParameterError> {
        let name_map = self.merged_name_map(rhs)?;
        Ok(Self {
            expr: &self.expr + &rhs.expr,
            name_map,
        })
    }

    /// Multiply with an expression; ``self * rhs``.
    pub fn mul(&self, rhs: &ParameterExpression) -> Result<Self, ParameterError> {
        let name_map = self.merged_name_map(rhs)?;
        Ok(Self {
            expr: &self.expr * &rhs.expr,
            name_map,
        })
    }

    /// Subtract another expression; ``self - rhs``.
    pub fn sub(&self, rhs: &ParameterExpression) -> Result<Self, ParameterError> {
        let name_map = self.merged_name_map(rhs)?;
        Ok(Self {
            expr: &self.expr - &rhs.expr,
            name_map,
        })
    }

    /// Divide by another expression; ``self / rhs``.
    pub fn div(&self, rhs: &ParameterExpression) -> Result<Self, ParameterError> {
        if rhs.expr.is_zero() {
            return Err(ParameterError::ZeroDivisionError);
        }

        let name_map = self.merged_name_map(rhs)?;
        Ok(Self {
            expr: &self.expr / &rhs.expr,
            name_map,
        })
    }

    /// Raise this expression to a power; ``self ^ rhs``.
    pub fn pow(&self, rhs: &ParameterExpression) -> Result<Self, ParameterError> {
        let name_map = self.merged_name_map(rhs)?;
        Ok(Self {
            expr: self.expr.pow(&rhs.expr),
            name_map,
        })
    }

    /// Apply the sine to this expression; ``sin(self)``.
    pub fn sin(&self) -> Self {
        Self {
            expr: self.expr.sin(),
            name_map: self.name_map.clone(),
        }
    }

    /// Apply the cosine to this expression; ``cos(self)``.
    pub fn cos(&self) -> Self {
        Self {
            expr: self.expr.cos(),
            name_map: self.name_map.clone(),
        }
    }

    /// Apply the tangent to this expression; ``tan(self)``.
    pub fn tan(&self) -> Self {
        Self {
            expr: self.expr.tan(),
            name_map: self.name_map.clone(),
        }
    }

    /// Apply the arcsine to this expression; ``asin(self)``.
    pub fn asin(&self) -> Self {
        Self {
            expr: self.expr.asin(),
            name_map: self.name_map.clone(),
        }
    }

    /// Apply the arccosine to this expression; ``acos(self)``.
    pub fn acos(&self) -> Self {
        Self {
            expr: self.expr.acos(),
            name_map: self.name_map.clone(),
        }
    }

    /// Apply the arctangent to this expression; ``atan(self)``.
    pub fn atan(&self) -> Self {
        Self {
            expr: self.expr.atan(),
            name_map: self.name_map.clone(),
        }
    }

    /// Exponentiate this expression; ``exp(self)``.
    pub fn exp(&self) -> Self {
        Self {
            expr: self.expr.exp(),
            name_map: self.name_map.clone(),
        }
    }

    /// Take the (natural) logarithm of this expression; ``log(self)``.
    pub fn log(&self) -> Self {
        Self {
            expr: self.expr.log(),
            name_map: self.name_map.clone(),
        }
    }

    /// Take the absolute value of this expression; ``|self|``.
    pub fn abs(&self) -> Self {
        Self {
            expr: self.expr.abs(),
            name_map: self.name_map.clone(),
        }
    }

    /// Return the sign of this expression; ``sign(self)``.
    pub fn sign(&self) -> Self {
        Self {
            expr: self.expr.sign(),
            name_map: self.name_map.clone(),
        }
    }

    /// Complex conjugate the expression.
    pub fn conjugate(&self) -> Self {
        Self {
            expr: self.expr.conjugate(),
            name_map: self.name_map.clone(),
        }
    }

    /// negate the expression.
    pub fn neg(&self) -> Self {
        Self {
            expr: -&self.expr,
            name_map: self.name_map.clone(),
        }
    }

    /// Compute the derivative of the expression with respect to the provided symbol.
    ///
    /// Note that this keeps the name map unchanged. Meaning that computing the derivative
    /// of ``x`` will yield ``1`` but the expression still owns the symbol ``x``. This is
    /// done such that we can still bind the value ``x`` in an automated process.
    pub fn derivative(&self, param: &Symbol) -> Result<Self, ParameterError> {
        Ok(Self {
            expr: self
                .expr
                .derivative(param)
                .map_err(ParameterError::DerivativeNotSupported)?,
            name_map: self.name_map.clone(),
        })
    }

    /// Substitute symbols with [ParameterExpression]s.
    ///
    /// # Arguments
    ///
    /// * map - A hashmap with [Symbol] keys and [ParameterExpression]s to replace these
    ///   symbols with.
    /// * allow_unknown_parameters - If `false`, returns an error if any symbol in the
    ///   hashmap is not present in the expression. If `true`, unknown symbols are ignored.
    ///   Setting to `true` is slightly faster as it does not involve additional checks.
    ///
    /// # Returns
    ///
    /// * `Ok(Self)` - A parameter expression with the substituted expressions.
    /// * `Err(ParameterError)` - An error if the substitution failed.
    pub fn subs(
        &self,
        map: &HashMap<Symbol, Self>,
        allow_unknown_parameters: bool,
    ) -> Result<Self, ParameterError> {
        // Build the outgoing name map. In the process we check for any duplicates.
        let mut name_map: HashMap<String, Symbol> = HashMap::new();
        let mut symbol_map: HashMap<Symbol, SymbolExpr> = HashMap::new();

        // If we don't allow for unknown parameters, check if there are any.
        if !allow_unknown_parameters {
            let existing: HashSet<&Symbol> = self.name_map.values().collect();
            let to_replace: HashSet<&Symbol> = map.keys().collect();
            let mut difference = to_replace.difference(&existing).peekable();

            if difference.peek().is_some() {
                let different_symbols = difference.map(|s| (**s).clone()).collect();
                return Err(ParameterError::UnknownParameters(different_symbols));
            }
        }

        for (name, symbol) in self.name_map.iter() {
            // check if the symbol will get replaced
            if let Some(replacement) = map.get(symbol) {
                // If yes, update the name_map. This also checks for duplicates.
                for (replacement_name, replacement_symbol) in replacement.name_map.iter() {
                    if let Some(duplicate) = name_map.get(replacement_name) {
                        // If a symbol with the same name already exists, check whether it is
                        // the same symbol (fine) or a different symbol with the same name (conflict)!
                        if duplicate != replacement_symbol {
                            return Err(ParameterError::NameConflict);
                        }
                    } else {
                        // SAFETY: We know the key does not exist yet.
                        unsafe {
                            name_map.insert_unique_unchecked(
                                replacement_name.clone(),
                                replacement_symbol.clone(),
                            )
                        };
                    }
                }

                // If we got until here, there were no duplicates, so we are safe to
                // add this symbol to the internal replacement map.
                symbol_map.insert(symbol.clone(), replacement.expr.clone());
            } else {
                // no replacement for this symbol, carry on
                match name_map.entry(name.clone()) {
                    Entry::Occupied(duplicate) => {
                        if duplicate.get() != symbol {
                            return Err(ParameterError::NameConflict);
                        }
                    }
                    Entry::Vacant(e) => {
                        e.insert(symbol.clone());
                    }
                }
            }
        }

        let res = self.expr.subs(&symbol_map);
        Ok(Self {
            expr: res,
            name_map,
        })
    }

    /// Bind symbols to values.
    ///
    /// # Arguments
    ///
    /// * map - A hashmap with [Symbol] keys and [Value]s to replace these
    ///   symbols with.
    /// * allow_unknown_parameter - If `false`, returns an error if any symbol in the
    ///   hashmap is not present in the expression. If `true`, unknown symbols are ignored.
    ///   Setting to `true` is slightly faster as it does not involve additional checks.
    ///
    /// # Returns
    ///
    /// * `Ok(Self)` - A parameter expression with the bound symbols.
    /// * `Err(ParameterError)` - An error if binding failed.
    pub fn bind(
        &self,
        map: &HashMap<&Symbol, Value>,
        allow_unknown_parameters: bool,
    ) -> Result<Self, ParameterError> {
        // The set of symbols we will bind. Used twice, hence pre-computed here.
        let bind_symbols: HashSet<&Symbol> = map.keys().cloned().collect();

        // If we don't allow for unknown parameters, check if there are any.
        if !allow_unknown_parameters {
            let existing: HashSet<&Symbol> = self.name_map.values().collect();
            let mut difference = bind_symbols.difference(&existing).peekable();

            if difference.peek().is_some() {
                let different_symbols = difference.map(|s| (**s).clone()).collect();
                return Err(ParameterError::UnknownParameters(different_symbols));
            }
        }

        // bind the symbol expression and then check the outcome for inf/nan, or numeric values
        let bound_expr = self.expr.bind(map);
        let bound = match bound_expr.eval(true) {
            Some(v) => match &v {
                Value::Real(r) => {
                    if r.is_infinite() {
                        Err(ParameterError::BindingInf)
                    } else if r.is_nan() {
                        Err(ParameterError::BindingNaN)
                    } else {
                        Ok(SymbolExpr::Value(v))
                    }
                }
                Value::Int(_) => Ok(SymbolExpr::Value(v)),
                Value::Complex(c) => {
                    if c.re.is_infinite() || c.im.is_infinite() {
                        Err(ParameterError::BindingInf)
                    } else if c.re.is_nan() || c.im.is_nan() {
                        Err(ParameterError::BindingNaN)
                    } else if (-symbol_expr::SYMEXPR_EPSILON..symbol_expr::SYMEXPR_EPSILON)
                        .contains(&c.im)
                    {
                        Ok(SymbolExpr::Value(Value::Real(c.re)))
                    } else {
                        Ok(SymbolExpr::Value(v))
                    }
                }
            },
            None => Ok(bound_expr),
        }?;

        // update the name map by removing the bound parameters
        let bound_name_map: HashMap<String, Symbol> = self
            .name_map
            .iter()
            .filter(|(_, symbol)| !bind_symbols.contains(symbol))
            .map(|(name, symbol)| (name.clone(), symbol.clone()))
            .collect();

        Ok(Self {
            expr: bound,
            name_map: bound_name_map,
        })
    }

    /// Merge name maps.
    ///
    /// # Arguments
    ///
    /// * `other` - The other parameter expression whose symbols we add to self.
    ///
    /// # Returns
    ///
    /// * `Ok(HashMap<String, Symbol>)` - The merged name map.
    /// * `Err(ParameterError)` - An error if there was a name conflict.
    fn merged_name_map(&self, other: &Self) -> Result<HashMap<String, Symbol>, ParameterError> {
        let mut merged = self.name_map.clone();
        for (name, param) in other.name_map.iter() {
            match merged.get(name) {
                Some(existing_param) => {
                    if param != existing_param {
                        return Err(ParameterError::NameConflict);
                    }
                }
                None => {
                    // SAFETY: We ensured the key is unique
                    let _ = unsafe { merged.insert_unique_unchecked(name.clone(), param.clone()) };
                }
            }
        }
        Ok(merged)
    }
}

/// A parameter expression.
///
/// This is backed by Qiskit's symbolic expression engine and a cache
/// for the parameters inside the expression.
#[pyclass(
    subclass,
    module = "qiskit._accelerate.circuit",
    name = "ParameterExpression",
    from_py_object
)]
#[derive(Clone, Debug)]
pub struct PyParameterExpression {
    pub inner: ParameterExpression,
}

impl Default for PyParameterExpression {
    /// The default constructor returns zero.
    fn default() -> Self {
        Self {
            inner: ParameterExpression::default(),
        }
    }
}

impl fmt::Display for PyParameterExpression {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        self.inner.fmt(f)
    }
}

impl From<ParameterExpression> for PyParameterExpression {
    fn from(value: ParameterExpression) -> Self {
        Self { inner: value }
    }
}

impl PyParameterExpression {
    /// Attempt to extract a `PyParameterExpression` from a bound `PyAny`.
    ///
    /// This will try to coerce to the strictest data type:
    /// Int - Real - Complex - PyParameterVectorElement - PyParameter - PyParameterExpression.
    ///
    /// # Arguments:
    ///
    /// * ob - The bound `PyAny` to extract from.
    ///
    /// # Returns
    ///
    /// * `Ok(Self)` - The extracted expression.
    /// * `Err(PyResult)` - An error if extraction to all above types failed.
    pub fn extract_coerce(ob: Borrowed<PyAny>) -> PyResult<Self> {
        if let Ok(i) = ob.cast::<PyInt>() {
            Ok(ParameterExpression::new(
                SymbolExpr::Value(Value::from(i.extract::<i64>()?)),
                HashMap::new(),
            )
            .into())
        } else if let Ok(r) = ob.cast::<PyFloat>() {
            let r: f64 = r.extract()?;
            if r.is_infinite() || r.is_nan() {
                return Err(ParameterError::InvalidValue.into());
            }
            Ok(ParameterExpression::new(SymbolExpr::Value(Value::from(r)), HashMap::new()).into())
        } else if let Ok(c) = ob.cast::<PyComplex>() {
            let c: Complex64 = c.extract()?;
            if c.is_infinite() || c.is_nan() {
                return Err(ParameterError::InvalidValue.into());
            }
            Ok(ParameterExpression::new(SymbolExpr::Value(Value::from(c)), HashMap::new()).into())
        } else if let Ok(element) = ob.cast::<PyParameterVectorElement>() {
            Ok(ParameterExpression::from_symbol(element.borrow().symbol.clone()).into())
        } else if let Ok(parameter) = ob.cast::<PyParameter>() {
            Ok(ParameterExpression::from_symbol(parameter.borrow().symbol.clone()).into())
        } else {
            ob.extract::<PyParameterExpression>().map_err(Into::into)
        }
    }

    pub fn coerce_into_py(&self, py: Python) -> PyResult<Py<PyAny>> {
        if let Ok(value) = self.inner.try_to_value(true) {
            match value {
                Value::Int(i) => Ok(PyInt::new(py, i).unbind().into_any()),
                Value::Real(r) => Ok(PyFloat::new(py, r).unbind().into_any()),
                Value::Complex(c) => Ok(PyComplex::from_complex_bound(py, c).unbind().into_any()),
            }
        } else if let Ok(symbol) = self.inner.try_to_symbol() {
            if symbol.index.is_some() {
                Ok(Py::new(py, PyParameterVectorElement::from_symbol(symbol))?.into_any())
            } else {
                Ok(Py::new(py, PyParameter::from_symbol(symbol))?.into_any())
            }
        } else {
            self.clone().into_py_any(py)
        }
    }
}

#[pymethods]
impl PyParameterExpression {
    /// This is a **strictly internal** constructor and **should not be used**.
    /// It is subject to arbitrary change in between Qiskit versions and cannot be relied on.
    /// Parameter expressions should always be constructed from applying operations on
    /// parameters, or by loading via QPY.
    ///
    /// The input values are allowed to be None for pickling purposes.
    #[new]
    #[pyo3(signature = (name_map=None, expr=None))]
    pub fn py_new(
        name_map: Option<HashMap<String, PyParameter>>,
        expr: Option<String>,
    ) -> PyResult<Self> {
        match (name_map, expr) {
            (None, None) => Ok(Self::default()),
            (Some(name_map), Some(expr)) => {
                // We first parse the expression and then update the symbols with the ones
                // the user provided. The replacement relies on the names to match.
                // This is hacky and we likely want a more reliably conversion from a SymPy object,
                // if we decide we want to continue supporting this.
                let expr = parse_expression(&expr)
                    .map_err(|_| PyRuntimeError::new_err("Failed parsing input expression"))?;
                let symbol_map: HashMap<String, Symbol> = name_map
                    .iter()
                    .map(|(string, param)| (string.clone(), param.symbol.clone()))
                    .collect();

                let replaced_expr = symbol_expr::replace_symbol(&expr, &symbol_map);

                let inner = ParameterExpression::new(replaced_expr, symbol_map);
                Ok(Self { inner })
            }
            _ => Err(PyValueError::new_err(
                "Pass either both a name_map and expr, or neither",
            )),
        }
    }

    #[allow(non_snake_case)]
    #[staticmethod]
    pub fn _Value(value: &Bound<PyAny>) -> PyResult<Self> {
        Self::extract_coerce(value.as_borrowed())
    }

    /// Check if the expression corresponds to a plain symbol.
    ///
    /// Returns:
    ///     ``True`` is this expression corresponds to a symbol, ``False`` otherwise.
    pub fn is_symbol(&self) -> bool {
        matches!(self.inner.expr, SymbolExpr::Symbol(_))
    }

    /// Cast this expression to a numeric value.
    ///
    /// Args:
    ///     strict: If ``True`` (default) this function raises an error if there are any
    ///         unbound symbols in the expression. If ``False``, this allows casting
    ///         if the expression represents a numeric value, regardless of unbound symbols.
    ///         For example ``(0 * Parameter("x"))`` is 0 but has the symbol ``x`` present.
    #[pyo3(signature = (strict=true))]
    pub fn numeric(&self, py: Python, strict: bool) -> PyResult<Py<PyAny>> {
        match self.inner.try_to_value(strict)? {
            Value::Real(r) => r.into_py_any(py),
            Value::Int(i) => i.into_py_any(py),
            Value::Complex(c) => c.into_py_any(py),
        }
    }

    /// Return a SymPy equivalent of this expression.
    ///
    /// Returns:
    ///     A SymPy equivalent of this expression.
    pub fn sympify(&self, py: Python) -> PyResult<Py<PyAny>> {
        let py_sympify = SYMPIFY_PARAMETER_EXPRESSION.get(py);
        py_sympify.call1(py, (self.clone(),))
    }

    /// The number of unbound parameters in the expression.
    ///
    /// This is equivalent to ``len(expr.parameters)`` but does not involve the overhead of creating
    /// a set and counting its length.
    #[getter]
    pub fn num_parameters(&self) -> usize {
        self.inner.num_symbols()
    }

    /// Get the parameters present in the expression.
    ///
    /// .. note::
    ///
    ///     Qiskit guarantees equality (via ``==``) of parameters retrieved from an expression
    ///     with the original :class:`.Parameter` objects used to create this expression,
    ///     but does **not guarantee** ``is`` comparisons to succeed.
    ///
    #[getter]
    pub fn parameters<'py>(&self, py: Python<'py>) -> PyResult<Bound<'py, PySet>> {
        let py_parameters: Vec<Py<PyAny>> = self
            .inner
            .iter_symbols()
            .map(|symbol| {
                if symbol.is_vector_element() {
                    Ok(
                        Py::new(py, PyParameterVectorElement::from_symbol(symbol.clone()))?
                            .into_any(),
                    )
                } else {
                    Ok(Py::new(py, PyParameter::from_symbol(symbol.clone()))?.into_any())
                }
            })
            .collect::<PyResult<_>>()?;
        PySet::new(py, py_parameters)
    }

    /// Sine of the expression.
    #[inline]
    #[pyo3(name = "sin")]
    pub fn py_sin(&self) -> Self {
        self.inner.sin().into()
    }

    /// Cosine of the expression.
    #[inline]
    #[pyo3(name = "cos")]
    pub fn py_cos(&self) -> Self {
        self.inner.cos().into()
    }

    /// Tangent of the expression.
    #[inline]
    #[pyo3(name = "tan")]
    pub fn py_tan(&self) -> Self {
        self.inner.tan().into()
    }

    /// Arcsine of the expression.
    #[inline]
    pub fn arcsin(&self) -> Self {
        self.inner.asin().into()
    }

    /// Arccosine of the expression.
    #[inline]
    pub fn arccos(&self) -> Self {
        self.inner.acos().into()
    }

    /// Arctangent of the expression.
    #[inline]
    pub fn arctan(&self) -> Self {
        self.inner.atan().into()
    }

    /// Exponentiate the expression.
    #[inline]
    #[pyo3(name = "exp")]
    pub fn py_exp(&self) -> Self {
        self.inner.exp().into()
    }

    /// Take the natural logarithm of the expression.
    #[inline]
    #[pyo3(name = "log")]
    pub fn py_log(&self) -> Self {
        self.inner.log().into()
    }

    /// Take the absolute value of the expression.
    #[inline]
    #[pyo3(name = "abs")]
    pub fn py_abs(&self) -> Self {
        self.inner.abs().into()
    }

    /// Return the sign of the expression.
    #[inline]
    #[pyo3(name = "sign")]
    pub fn py_sign(&self) -> Self {
        self.inner.sign().into()
    }

    /// Return the complex conjugate of the expression.
    #[inline]
    #[pyo3(name = "conjugate")]
    pub fn py_conjugate(&self) -> Self {
        self.inner.conjugate().into()
    }

    /// Check whether the expression represents a real number.
    ///
    /// Note that this will return ``None`` if there are unbound parameters, in which case
    /// it cannot be determined whether the expression is real.
    #[inline]
    #[pyo3(name = "is_real")]
    pub fn py_is_real(&self) -> Option<bool> {
        self.inner.expr.is_real()
    }

    /// Return derivative of this expression with respect to the input parameter.
    ///
    /// Args:
    ///     param: The parameter with respect to which the derivative is calculated.
    ///
    /// Returns:
    ///     The derivative as either a constant numeric value or a symbolic
    ///     :class:`.ParameterExpression`.
    pub fn gradient(&self, param: &Bound<'_, PyAny>) -> PyResult<Py<PyAny>> {
        let symbol = symbol_from_py_parameter(param)?;
        let d_expr = self.inner.derivative(&symbol)?;

        // try converting to value and return as built-in numeric type
        match d_expr.try_to_value(false) {
            Ok(val) => match val {
                Value::Real(r) => r.into_py_any(param.py()),
                Value::Int(i) => i.into_py_any(param.py()),
                Value::Complex(c) => c.into_py_any(param.py()),
            },
            Err(_) => PyParameterExpression::from(d_expr).into_py_any(param.py()),
        }
    }

    /// Return all values in this equation.
    pub fn _values(&self, py: Python) -> PyResult<Vec<Py<PyAny>>> {
        self.inner
            .expr
            .values()
            .iter()
            .map(|val| match val {
                Value::Real(r) => r.into_py_any(py),
                Value::Int(i) => i.into_py_any(py),
                Value::Complex(c) => c.into_py_any(py),
            })
            .collect()
    }

    /// Returns a new expression with replacement parameters.
    ///
    /// Args:
    ///     parameter_map: Mapping from :class:`.Parameter`\ s in ``self`` to the
    ///         :class:`.ParameterExpression` instances with which they should be replaced.
    ///     allow_unknown_parameters: If ``False``, raises an error if ``parameter_map``
    ///         contains :class:`.Parameter`\ s in the keys outside those present in the expression.
    ///         If ``True``, any such parameters are simply ignored.
    ///
    /// Raises:
    ///     CircuitError:
    ///         - If parameter_map contains parameters outside those in self.
    ///         - If the replacement parameters in ``parameter_map`` would result in
    ///           a name conflict in the generated expression.
    ///
    /// Returns:
    ///     A new expression with the specified parameters replaced.
    #[pyo3(name = "subs")]
    #[pyo3(signature = (parameter_map, allow_unknown_parameters=false))]
    pub fn py_subs(
        &self,
        parameter_map: HashMap<PyParameter, Self>,
        allow_unknown_parameters: bool,
    ) -> PyResult<Self> {
        // reduce the map to a HashMap<Symbol, ParameterExpression>
        let map = parameter_map
            .into_iter()
            .map(|(param, expr)| Ok((param.symbol, expr.inner)))
            .collect::<PyResult<_>>()?;

        // apply to the inner expression
        match self.inner.subs(&map, allow_unknown_parameters) {
            Ok(subbed) => Ok(subbed.into()),
            Err(e) => Err(e.into()),
        }
    }

    /// Binds the provided set of parameters to their corresponding values.
    ///
    /// Args:
    ///     parameter_values: Mapping of :class:`.Parameter` instances to the numeric value to which
    ///         they will be bound.
    ///     allow_unknown_parameters: If ``False``, raises an error if ``parameter_values``
    ///         contains :class:`.Parameter`\ s in the keys outside those present in the expression.
    ///         If ``True``, any such parameters are simply ignored.
    ///
    /// Raises:
    ///     CircuitError:
    ///         - If parameter_values contains parameters outside those in self.
    ///         - If a non-numeric value is passed in ``parameter_values``.
    ///     ZeroDivisionError:
    ///         - If binding the provided values requires division by zero.
    ///
    /// Returns:
    ///     A new expression parameterized by any parameters which were not bound by
    ///     ``parameter_values``.
    #[pyo3(name = "bind")]
    #[pyo3(signature = (parameter_values, allow_unknown_parameters=false))]
    pub fn py_bind(
        &self,
        parameter_values: HashMap<PyParameter, Bound<PyAny>>,
        allow_unknown_parameters: bool,
    ) -> PyResult<Self> {
        // reduce the map to a HashMap<Symbol, Value>
        let map = parameter_values
            .iter()
            .map(|(param, value)| {
                let value = value.extract()?;
                Ok((param.symbol(), value))
            })
            .collect::<PyResult<_>>()?;

        // apply to the inner expression
        match self.inner.bind(&map, allow_unknown_parameters) {
            Ok(bound) => Ok(bound.into()),
            Err(e) => Err(e.into()),
        }
    }

    /// Bind all of the parameters in ``self`` to numeric values in the dictionary, returning a
    /// numeric value.
    ///
    /// This is a special case of :meth:`bind` which can reach higher performance.  It is no problem
    /// for the ``values`` dictionary to contain parameters that are not used in this expression;
    /// the expectation is that the same bindings dictionary will be fed to other expressions as
    /// well.
    ///
    /// It is an error to call this method with a ``values`` dictionary that does not bind all of
    /// the values, or to call this method with non-numeric values, but this is not explicitly
    /// checked, since this method is intended for performance-sensitive use.  Passing an incorrect
    /// dictionary may result in unexpected behavior.
    ///
    /// Unlike :meth:`bind`, this method will not raise an exception if non-finite floating-point
    /// values are encountered.
    ///
    /// Args:
    ///     values: mapping of parameters to numeric values.
    #[pyo3(name = "bind_all")]
    #[pyo3(signature = (values, *))]
    pub fn py_bind_all(&self, values: Bound<PyAny>) -> PyResult<Value> {
        let mut partial_map = HashMap::with_capacity(self.inner.name_map.len());
        for symbol in self.inner.name_map.values() {
            let py_parameter = symbol.clone().into_pyobject(values.py())?;
            partial_map.insert(symbol, values.get_item(py_parameter)?.extract()?);
        }
        let bound = self.inner.expr.bind(&partial_map);
        bound.eval(true).ok_or_else(|| {
            PyTypeError::new_err(format!(
                "binding did not produce a numeric quantity: {bound:?}"
            ))
        })
    }

    /// Assign one parameter to a value, which can either be numeric or another parameter
    /// expression.
    ///
    /// Args:
    ///     parameter: A parameter in this expression whose value will be updated.
    ///     value: The new value to bind to.
    ///
    /// Returns:
    ///     A new expression parameterized by any parameters which were not bound by assignment.
    #[pyo3(name = "assign")]
    pub fn py_assign(&self, parameter: PyParameter, value: &Bound<PyAny>) -> PyResult<Self> {
        if let Ok(expr) = value.cast::<Self>() {
            let map = [(parameter, expr.borrow().clone())].into_iter().collect();
            self.py_subs(map, false)
        } else if value.extract::<Value>().is_ok() {
            let map = [(parameter, value.clone())].into_iter().collect();
            self.py_bind(map, false)
        } else {
            Err(PyValueError::new_err(
                "Unexpected value in assign: {replacement:?}",
            ))
        }
    }

    #[inline]
    fn __copy__(slf: PyRef<Self>) -> PyRef<Self> {
        // ParameterExpression is immutable.
        slf
    }

    #[inline]
    fn __deepcopy__<'py>(slf: PyRef<'py, Self>, _memo: Bound<'py, PyAny>) -> PyRef<'py, Self> {
        // Everything a ParameterExpression contains is immutable.
        slf
    }

    pub fn __eq__(&self, rhs: &Bound<PyAny>) -> PyResult<bool> {
        if let Ok(rhs) = Self::extract_coerce(rhs.as_borrowed()) {
            match rhs.inner.expr {
                SymbolExpr::Value(v) => match self.inner.try_to_value(false) {
                    Ok(e) => Ok(e == v),
                    Err(_) => Ok(false),
                },
                _ => Ok(self.inner.expr == rhs.inner.expr),
            }
        } else {
            Ok(false)
        }
    }

    #[inline]
    pub fn __abs__(&self) -> Self {
        self.inner.abs().into()
    }

    #[inline]
    pub fn __pos__(&self) -> Self {
        self.clone()
    }

    pub fn __neg__(&self) -> Self {
        Self {
            inner: ParameterExpression::new(-&self.inner.expr, self.inner.name_map.clone()),
        }
    }

    pub fn __add__(&self, rhs: &Bound<PyAny>) -> PyResult<Self> {
        if let Ok(rhs) = Self::extract_coerce(rhs.as_borrowed()) {
            Ok(self.inner.add(&rhs.inner)?.into())
        } else {
            Err(pyo3::exceptions::PyTypeError::new_err(
                "Unsupported data type for __add__",
            ))
        }
    }

    pub fn __radd__(&self, lhs: &Bound<PyAny>) -> PyResult<Self> {
        if let Ok(lhs) = Self::extract_coerce(lhs.as_borrowed()) {
            Ok(lhs.inner.add(&self.inner)?.into())
        } else {
            Err(pyo3::exceptions::PyTypeError::new_err(
                "Unsupported data type for __radd__",
            ))
        }
    }

    pub fn __sub__(&self, rhs: &Bound<PyAny>) -> PyResult<Self> {
        if let Ok(rhs) = Self::extract_coerce(rhs.as_borrowed()) {
            Ok(self.inner.sub(&rhs.inner)?.into())
        } else {
            Err(pyo3::exceptions::PyTypeError::new_err(
                "Unsupported data type for __sub__",
            ))
        }
    }

    pub fn __rsub__(&self, lhs: &Bound<PyAny>) -> PyResult<Self> {
        if let Ok(lhs) = Self::extract_coerce(lhs.as_borrowed()) {
            Ok(lhs.inner.sub(&self.inner)?.into())
        } else {
            Err(pyo3::exceptions::PyTypeError::new_err(
                "Unsupported data type for __rsub__",
            ))
        }
    }

    pub fn __mul__<'py>(&self, rhs: &Bound<'py, PyAny>) -> PyResult<Bound<'py, PyAny>> {
        let py = rhs.py();
        if let Ok(rhs) = Self::extract_coerce(rhs.as_borrowed()) {
            match self.inner.mul(&rhs.inner) {
                Ok(result) => PyParameterExpression::from(result).into_bound_py_any(py),
                Err(e) => Err(PyErr::from(e)),
            }
        } else {
            PyNotImplemented::get(py).into_bound_py_any(py)
        }
    }

    pub fn __rmul__(&self, lhs: &Bound<PyAny>) -> PyResult<Self> {
        if let Ok(lhs) = Self::extract_coerce(lhs.as_borrowed()) {
            Ok(lhs.inner.mul(&self.inner)?.into())
        } else {
            Err(pyo3::exceptions::PyTypeError::new_err(
                "Unsupported data type for __rmul__",
            ))
        }
    }

    pub fn __truediv__(&self, rhs: &Bound<PyAny>) -> PyResult<Self> {
        if let Ok(rhs) = Self::extract_coerce(rhs.as_borrowed()) {
            Ok(self.inner.div(&rhs.inner)?.into())
        } else {
            Err(pyo3::exceptions::PyTypeError::new_err(
                "Unsupported data type for __truediv__",
            ))
        }
    }

    pub fn __rtruediv__(&self, lhs: &Bound<PyAny>) -> PyResult<Self> {
        if let Ok(lhs) = Self::extract_coerce(lhs.as_borrowed()) {
            Ok(lhs.inner.div(&self.inner)?.into())
        } else {
            Err(pyo3::exceptions::PyTypeError::new_err(
                "Unsupported data type for __rtruediv__",
            ))
        }
    }

    pub fn __pow__(&self, rhs: &Bound<PyAny>, _modulo: Option<i32>) -> PyResult<Self> {
        if let Ok(rhs) = Self::extract_coerce(rhs.as_borrowed()) {
            Ok(self.inner.pow(&rhs.inner)?.into())
        } else {
            Err(pyo3::exceptions::PyTypeError::new_err(
                "Unsupported data type for __pow__",
            ))
        }
    }

    pub fn __rpow__(&self, lhs: &Bound<PyAny>, _modulo: Option<i32>) -> PyResult<Self> {
        if let Ok(lhs) = Self::extract_coerce(lhs.as_borrowed()) {
            Ok(lhs.inner.pow(&self.inner)?.into())
        } else {
            Err(pyo3::exceptions::PyTypeError::new_err(
                "Unsupported data type for __rpow__",
            ))
        }
    }

    pub fn __int__(&self) -> PyResult<i64> {
        match self.inner.try_to_value(false)? {
            Value::Complex(_) => Err(PyTypeError::new_err(
                "Cannot cast complex parameter to int.",
            )),
            Value::Real(r) => {
                let rounded = r.floor();
                Ok(rounded as i64)
            }
            Value::Int(i) => Ok(i),
        }
    }

    pub fn __float__(&self) -> PyResult<f64> {
        match self.inner.try_to_value(false)? {
            Value::Complex(c) => {
                if c.im.abs() > SYMEXPR_EPSILON {
                    Err(PyTypeError::new_err(
                        "Could not cast complex parameter expression to float.",
                    ))
                } else {
                    Ok(c.re)
                }
            }
            Value::Real(r) => Ok(r),
            Value::Int(i) => Ok(i as f64),
        }
    }

    pub fn __complex__(&self) -> PyResult<Complex64> {
        match self.inner.try_to_value(false)? {
            Value::Complex(c) => Ok(c),
            Value::Real(r) => Ok(Complex64::new(r, 0.)),
            Value::Int(i) => Ok(Complex64::new(i as f64, 0.)),
        }
    }

    pub fn __str__(&self) -> String {
        self.to_string()
    }

    pub fn __hash__(&self, py: Python) -> PyResult<u64> {
        match self.inner.try_to_value(false) {
            // if a value, we promise to match the hash of the raw value!
            Ok(value) => {
                let py_hash = BUILTIN_HASH.get_bound(py);
                match value {
                    Value::Complex(c) => py_hash.call1((c,))?.extract::<u64>(),
                    Value::Real(r) => py_hash.call1((r,))?.extract::<u64>(),
                    Value::Int(i) => py_hash.call1((i,))?.extract::<u64>(),
                }
            }
            Err(_) => {
                let mut hasher = DefaultHasher::new();
                self.inner.expr.string_id().hash(&mut hasher);
                Ok(hasher.finish())
            }
        }
    }

    fn __getstate__(&self) -> Vec<OPReplay> {
        self._qpy_replay()
    }

    fn __setstate__(&mut self, state: Vec<OPReplay>) -> PyResult<()> {
        self.inner = ParameterExpression::from_qpy(&state)?;
        Ok(())
    }

    #[getter]
    fn _qpy_replay(&self) -> Vec<OPReplay> {
        self.inner.qpy_replay()
    }
}

/// A compile-time symbolic parameter.
///
/// The value of a :class:`.Parameter` must be entirely determined before a circuit begins execution.
/// Typically this will mean that you should supply values for all :class:`.Parameter`\ s in a
/// circuit using :meth:`.QuantumCircuit.assign_parameters`, though certain hardware vendors may
/// allow you to give them a circuit in terms of these parameters, provided you also pass the values
/// separately.
///
/// This is the atom of :class:`.ParameterExpression`, and is itself an expression.  The numeric
/// value of a parameter need not be fixed while the circuit is being defined.
///
/// Examples:
///
///     Construct a variable-rotation X gate using circuit parameters.
///
///     .. plot::
///         :alt: Circuit diagram output by the previous code.
///         :include-source:
///
///         from qiskit.circuit import QuantumCircuit, Parameter
///
///         # create the parameter
///         phi = Parameter("phi")
///         qc = QuantumCircuit(1)
///
///         # parameterize the rotation
///         qc.rx(phi, 0)
///         qc.draw("mpl")
///
///         # bind the parameters after circuit to create a bound circuit
///         bc = qc.assign_parameters({phi: 3.14})
///         bc.measure_all()
///         bc.draw("mpl")
#[pyclass(
    sequence,
    subclass,
    module="qiskit._accelerate.circuit",
    extends=PyParameterExpression,
    name="Parameter",
    from_py_object
)]
#[derive(Clone, Debug, PartialEq, Eq, PartialOrd)]
pub struct PyParameter {
    pub symbol: Symbol,
}

impl Hash for PyParameter {
    fn hash<H: Hasher>(&self, state: &mut H) {
        self.symbol.hash(state);
    }
}

// This needs to be implemented manually, since PyO3 does not provide this conversion
// for subclasses.
impl<'py> IntoPyObject<'py> for PyParameter {
    type Target = PyParameter;
    type Output = Bound<'py, Self::Target>;
    type Error = PyErr;

    fn into_pyobject(self, py: Python<'py>) -> Result<Self::Output, Self::Error> {
        let symbol = &self.symbol;
        let symbol_expr = SymbolExpr::Symbol(Arc::new(symbol.clone()));
        let expr = ParameterExpression::from_symbol_expr(symbol_expr);
        let py_expr = PyParameterExpression::from(expr);

        Ok(Py::new(py, (self, py_expr))?.into_bound(py))
    }
}

impl PyParameter {
    /// Get a Python class initialization from a symbol.
    pub fn from_symbol(symbol: Symbol) -> PyClassInitializer<Self> {
        let expr = SymbolExpr::Symbol(Arc::new(symbol.clone()));

        let py_parameter = Self { symbol };
        let py_expr: PyParameterExpression = ParameterExpression::from_symbol_expr(expr).into();

        PyClassInitializer::from(py_expr).add_subclass(py_parameter)
    }

    /// Get a reference to the underlying symbol.
    pub fn symbol(&self) -> &Symbol {
        &self.symbol
    }
}

#[pymethods]
impl PyParameter {
    /// Args:
    ///     name: name of the parameter, used for visual representation. This can
    ///         be any Unicode string, e.g. ``"ϕ"``.
    ///     uuid: For advanced usage only.  Override the UUID of this parameter, in order to make it
    ///         compare equal to some other parameter object.  By default, two parameters with the
    ///         same name do not compare equal to help catch shadowing bugs when two circuits
    ///         containing the same named parameters are spurious combined.  Setting the ``uuid``
    ///         field when creating two parameters to the same thing (along with the same name)
    ///         allows them to be equal.  This is useful during serialization and deserialization.
    #[new]
    #[pyo3(signature = (name, uuid=None))]
    fn py_new(
        py: Python<'_>,
        name: String,
        uuid: Option<Py<PyAny>>,
    ) -> PyResult<PyClassInitializer<Self>> {
        let uuid = uuid_from_py(py, uuid)?;
        let symbol = Symbol::new(name.as_str(), uuid, None);
        let expr = SymbolExpr::Symbol(Arc::new(symbol.clone()));

        let py_parameter = Self { symbol };
        let py_expr: PyParameterExpression = ParameterExpression::from_symbol_expr(expr).into();

        Ok(PyClassInitializer::from(py_expr).add_subclass(py_parameter))
    }

    /// Returns the name of the :class:`.Parameter`.
    #[getter]
    fn name<'py>(&self, py: Python<'py>) -> Bound<'py, PyString> {
        PyString::new(py, &self.symbol.repr(false))
    }

    /// Returns the :class:`~uuid.UUID` of the :class:`Parameter`.
    ///
    /// In advanced use cases, this property can be passed to the
    /// :class:`.Parameter` constructor to produce an instance that compares
    /// equal to another instance.
    #[getter]
    fn uuid(&self, py: Python<'_>) -> PyResult<Py<PyAny>> {
        uuid_to_py(py, self.symbol.uuid)
    }

    pub fn __repr__<'py>(&self, py: Python<'py>) -> Bound<'py, PyString> {
        let str = format!("Parameter({})", self.symbol.repr(false),);
        PyString::new(py, str.as_str())
    }

    pub fn __getnewargs__(&self) -> (String, u128) {
        (self.symbol.repr(false), self.symbol.uuid.as_u128())
    }

    pub fn __getstate__(&self) -> (String, u128) {
        (self.symbol.repr(false), self.symbol.uuid.as_u128())
    }

    pub fn __setstate__(&mut self, state: (String, u128)) {
        let name = state.0.as_str();
        let uuid = Uuid::from_u128(state.1);
        let symbol = Symbol::new(name, Some(uuid), None);
        self.symbol = symbol;
    }

    fn __copy__(slf: PyRef<Self>) -> PyRef<Self> {
        // Parameter is immutable. Note that this **cannot** be deferred to the parent class
        // since PyO3 would then always return the parent type.
        slf
    }

    fn __deepcopy__<'py>(slf: PyRef<'py, Self>, _memo: Bound<'py, PyAny>) -> PyRef<'py, Self> {
        // Everything inside a Parameter is immutable. Note that this **cannot** be deferred to the
        // parent class since PyO3 would then always return the parent type.
        slf
    }

    #[pyo3(name = "subs")]
    #[pyo3(signature = (parameter_map, allow_unknown_parameters=false))]
    pub fn py_subs<'py>(
        &self,
        py: Python<'py>,
        parameter_map: HashMap<PyParameter, Bound<'py, PyAny>>,
        allow_unknown_parameters: bool,
    ) -> PyResult<Bound<'py, PyAny>> {
        // We implement this method on this class, and do not defer to the parent, such
        // that x.subs({x: y}) remains a Parameter, and is not upgraded to an expression.
        // Also this should be faster than going via ParameterExpression, which constructs
        // intermediary HashMaps we don't need here.
        match parameter_map.get(self) {
            None => {
                if allow_unknown_parameters {
                    self.clone().into_bound_py_any(py)
                } else {
                    Err(CircuitError::new_err(
                        "Cannot bind parameters not present in parameter.",
                    ))
                }
            }
            Some(replacement) => {
                if allow_unknown_parameters || parameter_map.len() == 1 {
                    Ok(replacement.clone())
                } else {
                    Err(CircuitError::new_err(
                        "Cannot bind parameters not present in parameter.",
                    ))
                }
            }
        }
    }

    #[pyo3(name = "bind")]
    #[pyo3(signature = (parameter_values, allow_unknown_parameters=false))]
    pub fn py_bind<'py>(
        &self,
        py: Python<'py>,
        parameter_values: HashMap<PyParameter, Bound<'py, PyAny>>,
        allow_unknown_parameters: bool,
    ) -> PyResult<Bound<'py, PyAny>> {
        // Returns PyAny to cover Parameter and ParameterExpression(value).
        match parameter_values.get(self) {
            None => {
                if allow_unknown_parameters {
                    self.clone().into_bound_py_any(py)
                } else {
                    Err(CircuitError::new_err(
                        "Cannot bind parameters not present in parameter.",
                    ))
                }
            }
            Some(replacement) => {
                if allow_unknown_parameters || parameter_values.len() == 1 {
                    let expr = PyParameterExpression::extract_coerce(replacement.as_borrowed())?;
                    if let SymbolExpr::Value(_) = &expr.inner.expr {
                        expr.clone().into_bound_py_any(py)
                    } else {
                        Err(PyValueError::new_err("Invalid binding value."))
                    }
                } else {
                    Err(CircuitError::new_err(
                        "Cannot bind parameters not present in parameter.",
                    ))
                }
            }
        }
    }

    #[pyo3(name = "bind_all")]
    #[pyo3(signature = (values, *))]
    pub fn py_bind_all<'py>(
        slf_: Bound<'py, Self>,
        values: Bound<'py, PyAny>,
    ) -> PyResult<Bound<'py, PyAny>> {
        values.get_item(slf_)
    }

    #[pyo3(name = "assign")]
    pub fn py_assign<'py>(
        &self,
        py: Python<'py>,
        parameter: PyParameter,
        value: &Bound<'py, PyAny>,
    ) -> PyResult<Bound<'py, PyAny>> {
        if value.cast::<PyParameterExpression>().is_ok() {
            let map = [(parameter, value.clone())].into_iter().collect();
            self.py_subs(py, map, false)
        } else if value.extract::<Value>().is_ok() {
            let map = [(parameter, value.clone())].into_iter().collect();
            self.py_bind(py, map, false)
        } else {
            Err(PyValueError::new_err(
                "Unexpected value in assign: {replacement:?}",
            ))
        }
    }
}

/// An element of a :class:`.ParameterVector`.
///
/// .. note::
///     There is very little reason to ever construct this class directly.  Objects of this type are
///     automatically constructed efficiently as part of creating a :class:`.ParameterVector`.
#[pyclass(
    sequence,
    subclass,
    module="qiskit._accelerate.circuit",
    extends=PyParameter,
    name="ParameterVectorElement",
    from_py_object
)]
#[derive(Clone, Debug, Eq, PartialEq, PartialOrd)]
pub struct PyParameterVectorElement {
    pub symbol: Symbol,
}

impl<'py> IntoPyObject<'py> for PyParameterVectorElement {
    type Target = PyParameterVectorElement;
    type Output = Bound<'py, Self::Target>;
    type Error = PyErr;

    fn into_pyobject(self, py: Python<'py>) -> Result<Self::Output, Self::Error> {
        let symbol = &self.symbol;
        let py_param = PyParameter::from_symbol(symbol.clone());
        let py_element = py_param.add_subclass(self);

        Ok(Py::new(py, py_element)?.into_bound(py))
    }
}

impl PyParameterVectorElement {
    pub fn symbol(&self) -> &Symbol {
        &self.symbol
    }

    pub fn from_symbol(symbol: Symbol) -> PyClassInitializer<Self> {
        let py_element = Self {
            symbol: symbol.clone(),
        };
        let py_parameter = PyParameter::from_symbol(symbol);

        py_parameter.add_subclass(py_element)
    }
}

#[pymethods]
impl PyParameterVectorElement {
    #[new]
    #[pyo3(signature = (vector, index, uuid=None))]
    pub fn py_new(
        py: Python<'_>,
        vector: Py<PyAny>,
        index: u32,
        uuid: Option<Py<PyAny>>,
    ) -> PyResult<PyClassInitializer<Self>> {
        let vector_name = vector.getattr(py, "name")?.extract::<String>(py)?;
        let uuid = uuid_from_py(py, uuid)?.unwrap_or(Uuid::new_v4());

        let symbol = Symbol::py_new(
            &vector_name,
            Some(uuid.as_u128()),
            Some(index),
            Some(vector.clone_ref(py)),
        )?;

        let py_parameter = PyParameter::from_symbol(symbol.clone());
        let py_element = Self { symbol };

        Ok(py_parameter.add_subclass(py_element))
    }

    pub fn __getnewargs__(&self, py: Python) -> PyResult<(Py<PyAny>, u32, Option<Py<PyAny>>)> {
        let vector = self
            .symbol
            .vector
            .clone()
            .expect("vector element should have a vector");
        let index = self
            .symbol
            .index
            .expect("vector element should have an index");
        let uuid = uuid_to_py(py, self.symbol.uuid)?;
        Ok((vector, index, Some(uuid)))
    }

    pub fn __repr__<'py>(&self, py: Python<'py>) -> Bound<'py, PyString> {
        let str = format!("ParameterVectorElement({})", self.symbol.repr(false),);
        PyString::new(py, str.as_str())
    }

    pub fn __getstate__(&self, py: Python) -> PyResult<(Py<PyAny>, u32, Option<Py<PyAny>>)> {
        self.__getnewargs__(py)
    }

    pub fn __setstate__(
        &mut self,
        py: Python,
        state: (Py<PyAny>, u32, Option<Py<PyAny>>),
    ) -> PyResult<()> {
        let vector = state.0;
        let index = state.1;
        let vector_name = vector.getattr(py, "name")?.extract::<String>(py)?;
        let uuid = uuid_from_py(py, state.2)?.map(|id| id.as_u128());
        self.symbol = Symbol::py_new(&vector_name, uuid, Some(index), Some(vector))?;
        Ok(())
    }

    /// Get the index of this element in the parent vector.
    #[getter]
    pub fn index(&self) -> u32 {
        self.symbol
            .index
            .expect("A vector element should have an index")
    }

    /// Get the parent vector instance.
    #[getter]
    pub fn vector(&self) -> Py<PyAny> {
        self.symbol
            .clone()
            .vector
            .expect("A vector element should have a vector")
    }

    /// For backward compatibility only. This should not be used and we ought to update those
    /// usages!
    #[getter]
    pub fn _vector(&self) -> Py<PyAny> {
        self.vector()
    }

    fn __copy__(slf: PyRef<Self>) -> PyRef<Self> {
        // ParameterVectorElement is immutable.
        slf
    }

    fn __deepcopy__<'py>(slf: PyRef<'py, Self>, _memo: Bound<'py, PyAny>) -> PyRef<'py, Self> {
        // Everything a ParameterVectorElement contains is immutable.
        slf
    }
}

/// Try to extract a Uuid from a Python object, which could be a Python UUID or int.
fn uuid_from_py(py: Python<'_>, uuid: Option<Py<PyAny>>) -> PyResult<Option<Uuid>> {
    if let Some(val) = uuid {
        // construct from u128
        let as_u128 = if let Ok(as_u128) = val.extract::<u128>(py) {
            as_u128
        // construct from Python UUID type
        } else if val.bind(py).is_exact_instance(UUID.get_bound(py)) {
            val.getattr(py, "int")?.extract::<u128>(py)?
        // invalid format
        } else {
            return Err(PyTypeError::new_err("not a UUID!"));
        };
        Ok(Some(Uuid::from_u128(as_u128)))
    } else {
        Ok(None)
    }
}

/// Convert a Rust Uuid object to a Python UUID object.
fn uuid_to_py(py: Python<'_>, uuid: Uuid) -> PyResult<Py<PyAny>> {
    let uuid = uuid.as_u128();
    let kwargs = [("int", uuid)].into_py_dict(py)?;
    Ok(UUID.get_bound(py).call((), Some(&kwargs))?.unbind())
}

/// Extract a [Symbol] for a Python object, which could either be a Parameter or a
/// ParameterVectorElement.
fn symbol_from_py_parameter(param: &Bound<'_, PyAny>) -> PyResult<Symbol> {
    if let Ok(element) = param.extract::<PyParameterVectorElement>() {
        Ok(element.symbol.clone())
    } else if let Ok(parameter) = param.extract::<PyParameter>() {
        Ok(parameter.symbol.clone())
    } else {
        Err(PyValueError::new_err("Could not extract parameter"))
    }
}

/// A singular parameter value used for QPY serialization. This covers anything
/// but a [PyParameterExpression], which is represented by [None] in the serialization.
#[derive(IntoPyObject, FromPyObject, Clone, Debug)]
pub enum ParameterValueType {
    Int(i64),
    Float(f64),
    Complex(Complex64),
    Parameter(PyParameter),
    VectorElement(PyParameterVectorElement),
}

impl ParameterValueType {
    fn from_symbol(symbol: Symbol) -> Self {
        if symbol.index.is_some() {
            Self::VectorElement(PyParameterVectorElement { symbol })
        } else {
            Self::Parameter(PyParameter { symbol })
        }
    }
    fn extract_from_expr(expr: &SymbolExpr) -> Option<ParameterValueType> {
        if let Some(value) = expr.eval(true) {
            match value {
                Value::Int(i) => Some(ParameterValueType::Int(i)),
                Value::Real(r) => Some(ParameterValueType::Float(r)),
                Value::Complex(c) => Some(ParameterValueType::Complex(c)),
            }
        } else if let SymbolExpr::Symbol(symbol) = expr {
            Some(Self::from_symbol(symbol.as_ref().clone()))
        } else {
            // ParameterExpressions have the value None, as they must be constructed
            None
        }
    }
}

impl From<ParameterValueType> for ParameterExpression {
    fn from(value: ParameterValueType) -> Self {
        match value {
            ParameterValueType::Parameter(param) => {
                let expr = SymbolExpr::Symbol(Arc::new(param.symbol));
                Self::from_symbol_expr(expr)
            }
            ParameterValueType::VectorElement(param) => {
                let expr = SymbolExpr::Symbol(Arc::new(param.symbol));
                Self::from_symbol_expr(expr)
            }
            ParameterValueType::Int(i) => {
                let expr = SymbolExpr::Value(Value::Int(i));
                Self::from_symbol_expr(expr)
            }
            ParameterValueType::Float(f) => {
                let expr = SymbolExpr::Value(Value::Real(f));
                Self::from_symbol_expr(expr)
            }
            ParameterValueType::Complex(c) => {
                let expr = SymbolExpr::Value(Value::Complex(c));
                Self::from_symbol_expr(expr)
            }
        }
    }
}

#[pyclass(module = "qiskit._accelerate.circuit", from_py_object)]
#[derive(Clone, Copy, Debug, Eq, PartialEq, Hash, PartialOrd, Ord)]
#[repr(u8)]
pub enum OpCode {
    ADD = 0,
    SUB = 1,
    MUL = 2,
    DIV = 3,
    POW = 4,
    SIN = 5,
    COS = 6,
    TAN = 7,
    ASIN = 8,
    ACOS = 9,
    EXP = 10,
    LOG = 11,
    SIGN = 12,
    GRAD = 13, // for backward compatibility, unused in Rust's ParameterExpression
    CONJ = 14,
    SUBSTITUTE = 15, // for backward compatibility, unused in Rust's ParameterExpression
    ABS = 16,
    ATAN = 17,
    RSUB = 18,
    RDIV = 19,
    RPOW = 20,
}

impl From<OpCode> for u8 {
    fn from(value: OpCode) -> Self {
        value as u8
    }
}

unsafe impl ::bytemuck::CheckedBitPattern for OpCode {
    type Bits = u8;

    #[inline(always)]
    fn is_valid_bit_pattern(bits: &Self::Bits) -> bool {
        *bits <= 20
    }
}

unsafe impl ::bytemuck::NoUninit for OpCode {}

impl OpCode {
    pub fn from_u8(value: u8) -> PyResult<OpCode> {
        Ok(bytemuck::checked::cast::<u8, OpCode>(value))
    }
}

#[pymethods]
impl OpCode {
    #[new]
    fn py_new(value: u8) -> PyResult<Self> {
        let code: OpCode = ::bytemuck::checked::try_cast(value)
            .map_err(|_| ParameterError::InvalidU8ToOpCode(value))?;
        Ok(code)
    }

    fn __eq__(&self, other: &Bound<'_, PyAny>) -> bool {
        if let Ok(code) = other.cast::<OpCode>() {
            *code.borrow() == *self
        } else {
            false
        }
    }

    fn __hash__(&self) -> u8 {
        *self as u8
    }

    fn __getnewargs__(&self) -> (u8,) {
        (*self as u8,)
    }
}

// enum for QPY replay
#[pyclass(sequence, module = "qiskit._accelerate.circuit", from_py_object)]
#[derive(Clone, Debug)]
pub struct OPReplay {
    pub op: OpCode,
    pub lhs: Option<ParameterValueType>,
    pub rhs: Option<ParameterValueType>,
}

#[pymethods]
impl OPReplay {
    #[new]
    pub fn py_new(
        op: OpCode,
        lhs: Option<ParameterValueType>,
        rhs: Option<ParameterValueType>,
    ) -> OPReplay {
        OPReplay { op, lhs, rhs }
    }

    #[getter]
    fn op(&self) -> OpCode {
        self.op
    }

    #[getter]
    fn lhs(&self) -> Option<ParameterValueType> {
        self.lhs.clone()
    }

    #[getter]
    fn rhs(&self) -> Option<ParameterValueType> {
        self.rhs.clone()
    }

    fn __getnewargs__(
        &self,
    ) -> (
        OpCode,
        Option<ParameterValueType>,
        Option<ParameterValueType>,
    ) {
        (self.op, self.lhs.clone(), self.rhs.clone())
    }
}

/// Internal helper. Extract one part of the expression tree, keeping the name map up to date.
///
/// Example: Given expr1 + expr2, each being [PyParameterExpression], we need the ability to
/// extract one of the expressions with the proper name map.
///
/// Args:
///     - joint_parameter_expr: The full expression, e.g. expr1 + expr2.
///     - sub_expr: The sub expression, on whose symbols we restrict the name map.
fn filter_name_map(
    sub_expr: &SymbolExpr,
    name_map: &HashMap<String, Symbol>,
) -> ParameterExpression {
    let sub_symbols: HashSet<&Symbol> = sub_expr.iter_symbols().collect();
    let restricted_name_map: HashMap<String, Symbol> = name_map
        .iter()
        .filter(|(_, symbol)| sub_symbols.contains(*symbol))
        .map(|(name, symbol)| (name.clone(), symbol.clone()))
        .collect();

    ParameterExpression {
        expr: sub_expr.clone(),
        name_map: restricted_name_map,
    }
}

fn qpy_replay_inner(
    expr: &ParameterExpression,
    name_map: &HashMap<String, Symbol>,
    replay: &mut Vec<OPReplay>,
    unused: &mut IndexSet<Symbol, foldhash::fast::RandomState>,
) {
    match &expr.expr {
        // This function is written under the assumption that the top-level expression involves an
        // operation, since `OPReplay` items correspond to operations that own their operands.
        SymbolExpr::Value(_) => (),
        SymbolExpr::Symbol(sym) => {
            unused.swap_remove(sym.as_ref());
        }
        SymbolExpr::Unary { op, expr } => {
            let op = match op {
                symbol_expr::UnaryOp::Abs => OpCode::ABS,
                symbol_expr::UnaryOp::Acos => OpCode::ACOS,
                symbol_expr::UnaryOp::Asin => OpCode::ASIN,
                symbol_expr::UnaryOp::Atan => OpCode::ATAN,
                symbol_expr::UnaryOp::Conj => OpCode::CONJ,
                symbol_expr::UnaryOp::Cos => OpCode::COS,
                symbol_expr::UnaryOp::Exp => OpCode::EXP,
                symbol_expr::UnaryOp::Log => OpCode::LOG,
                symbol_expr::UnaryOp::Neg => OpCode::MUL,
                symbol_expr::UnaryOp::Sign => OpCode::SIGN,
                symbol_expr::UnaryOp::Sin => OpCode::SIN,
                symbol_expr::UnaryOp::Tan => OpCode::TAN,
            };
            // TODO filter shouldn't be necessary for unary ops
            let lhs = filter_name_map(expr, name_map);

            // recurse on the instruction
            qpy_replay_inner(&lhs, name_map, replay, unused);

            let lhs_value = ParameterValueType::extract_from_expr(expr);

            // MUL is special: we implement ``neg`` as multiplication by -1
            if let OpCode::MUL = &op {
                replay.push(OPReplay {
                    op,
                    lhs: lhs_value,
                    rhs: Some(ParameterValueType::Int(-1)),
                });
            } else {
                replay.push(OPReplay {
                    op,
                    lhs: lhs_value,
                    rhs: None,
                });
            }
        }
        SymbolExpr::Binary { op, lhs, rhs } => {
            let lhs_value = ParameterValueType::extract_from_expr(lhs);
            let rhs_value = ParameterValueType::extract_from_expr(rhs);

            // recurse on the parameter expressions
            let lhs = filter_name_map(lhs, name_map);
            let rhs = filter_name_map(rhs, name_map);
            qpy_replay_inner(&lhs, name_map, replay, unused);
            qpy_replay_inner(&rhs, name_map, replay, unused);

            // add the expression to the replay
            match lhs_value {
                Some(ParameterValueType::Parameter(_))
                | Some(ParameterValueType::VectorElement(_)) => {
                    // For non-commutative operations (SUB, DIV, POW): if LHS is a Parameter and RHS is
                    // an expression (None), we need to use reverse operations (RSUB, RDIV, RPOW)
                    let op = match op {
                        symbol_expr::BinaryOp::Add => OpCode::ADD,
                        symbol_expr::BinaryOp::Sub => {
                            // If RHS is None (an expression), use RSUB
                            if rhs_value.is_none() {
                                OpCode::RSUB
                            } else {
                                OpCode::SUB
                            }
                        }
                        symbol_expr::BinaryOp::Mul => OpCode::MUL,
                        symbol_expr::BinaryOp::Div => {
                            // If RHS is None (an expression), use RDIV
                            if rhs_value.is_none() {
                                OpCode::RDIV
                            } else {
                                OpCode::DIV
                            }
                        }
                        symbol_expr::BinaryOp::Pow => {
                            // If RHS is None (an expression), use RPOW
                            if rhs_value.is_none() {
                                OpCode::RPOW
                            } else {
                                OpCode::POW
                            }
                        }
                    };
                    if op == OpCode::RPOW || op == OpCode::RDIV || op == OpCode::RSUB {
                        // For reverse operations, swap lhs and rhs (Python's sympify will swap again to get correct order)
                        replay.push(OPReplay {
                            op,
                            lhs: rhs_value,
                            rhs: lhs_value,
                        });
                    } else {
                        replay.push(OPReplay {
                            op,
                            lhs: lhs_value,
                            rhs: rhs_value,
                        });
                    }
                }
                None => {
                    // When LHS is an expression (None), use normal operations
                    let op = match op {
                        symbol_expr::BinaryOp::Add => OpCode::ADD,
                        symbol_expr::BinaryOp::Sub => OpCode::SUB,
                        symbol_expr::BinaryOp::Mul => OpCode::MUL,
                        symbol_expr::BinaryOp::Div => OpCode::DIV,
                        symbol_expr::BinaryOp::Pow => OpCode::POW,
                    };
                    replay.push(OPReplay {
                        op,
                        lhs: lhs_value,
                        rhs: rhs_value,
                    });
                }
                _ => {
                    let op = match op {
                        symbol_expr::BinaryOp::Add => OpCode::ADD,
                        symbol_expr::BinaryOp::Sub => OpCode::RSUB,
                        symbol_expr::BinaryOp::Mul => OpCode::MUL,
                        symbol_expr::BinaryOp::Div => OpCode::RDIV,
                        symbol_expr::BinaryOp::Pow => OpCode::RPOW,
                    };
                    if let OpCode::ADD | OpCode::MUL = op {
                        replay.push(OPReplay {
                            op,
                            lhs: lhs_value,
                            rhs: rhs_value,
                        });
                    } else {
                        // this covers RSUB, RDIV, RPOW, hence we swap lhs and rhs
                        replay.push(OPReplay {
                            op,
                            lhs: rhs_value,
                            rhs: lhs_value,
                        });
                    }
                }
            }
        }
    }
}

Qiskit / qiskit / 25723423515

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