quantopian / zipline / 2717

88%

Pull #521

travis-ci

align internal representation to UTC

  When calculate trading_days in RiskMetricsCumulative with days_in_range(),
if the start/end days are in local timezone, the first day will be omitted.
The problem is:
```
>>> import pandas as pd
>>> dt = pd.to_datetime("2015-03-03 09:30:00")
>>> dt_localized = dt.tz_localize("US/Eastern")
>>> dt_localized.replace(hour=0,minute=0)
Timestamp('2015-03-03 00:00:00-0500', tz='US/Eastern')
>>> dt.replace(hour=0,minute=0)
Timestamp('2015-03-03 00:00:00')
```
  I think it might be less mind-twisted to represent the datetime in
market timezone internally.

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