aio-libs / multidict / 35776927198

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Do not swallow errors raised while sizing an update argument (#1517)

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## What do these changes do?

`_multidict_extend_parse_args()` cleared every pending exception when
`PyObject_LengthHint()` failed on the positional argument, so a
`MemoryError` or `KeyboardInterrupt` raised by that object's `__len__`
was discarded and the update simply went ahead with no size estimate.
The fallback is now guarded with `PyErr_ExceptionMatches()`, so only the
`TypeError` from an unusable `__length_hint__` is ignored. That is the
same pattern the sibling probes picked up in #1382.

`PyObject_LengthHint()` already absorbs a missing `__len__` or
`__length_hint__` internally, so the only `TypeError` that reaches this
branch is "`__length_hint__` must be an integer"; a broken hint costs
the preallocation estimate and nothing else, so it stays ignored.

C-extension only. The pure-Python backend reaches `__len__` through a
plain truth test and already propagates, so this closes a divergence
rather than creating one. Plain `MultiDict(arg)` is unaffected on either
backend: its vectorcall path never probes the argument's length, so only
`extend()`, `update()`, `merge()` and subclass construction ever reached
the cleared branch.

## Are there changes in behavior for the user?

Yes, in an edge case. `extend()`, `update()`, `merge()` and subclass
construction now propagate a `MemoryError` or `KeyboardInterrupt` raised
by the argument's `__len__` instead of swallowing it. Arguments without
a
usable length, the common case for a generator, are unchanged.

## Is it a substantial burden for the maintainers to support this?

No. It applies the module's existing guard pattern to the one site that
still missed it.

## Related issue number

Findings from the C-extension analysis report #1306. This was the last
open item from that report; everything else in it is already fixed on
master, so #1306 can probably be closed once this lands.

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