freeze_time might leave some instances patched after exit

Module A gets imported inside freeze_time context manager Module A imports datetime.datetime (patched with freezegun). Context manager exists and unpatches all modules it has tracked in undo_changes.

The problem is that module A still has FakeDatetime instead of datetime.datetime, which results in something like that if it gets called:

    return cls.times_to_freeze[-1]
IndexError: list index out of range

Sorry, I have no test to show this bug.

[GDICommander]

I have the same issue with 0.3.7, I am using a pytest fixture that uses “freeze_time”:

@pytest.yield_fixture
def frozen_clock():
    with freeze_time("2012-01-14 12:00:01.123"):
        yield

One of the tests that does not use this fixture hits this issue when using structlog and datetime.utcnow():

rdv_load_test_agent\tunnel.py:475: in load
    data = await self._send_message('LOAD', path=bpt_file)
C:\Python35\Lib\contextlib.py:77: in __exit__
    self.gen.throw(type, value, traceback)
rdv_load_test_agent\tunnel.py:112: in monitor_transaction
    event_log.info(event, outcome=outcome, duration=duration, **kwds)
..\venvs\rdv_lta_pagagne\lib\site-packages\structlog\_base.py:176: in _proxy_to_logger
    args, kw = self._process_event(method_name, event, event_kw)
..\venvs\rdv_lta_pagagne\lib\site-packages\structlog\_base.py:136: in _process_event
    event_dict = proc(self._logger, method_name, event_dict)
..\venvs\rdv_lta_pagagne\lib\site-packages\structlog\processors.py:213: in stamper
    event_dict[key] = now_method().isoformat() + 'Z'
..\venvs\rdv_lta_pagagne\lib\site-packages\freezegun\api.py:191: in utcnow
    result = cls._time_to_freeze()

cls = <class 'freezegun.api.FakeDatetime'>

    @classmethod
    def _time_to_freeze(cls):
>       return cls.times_to_freeze[-1]()
E       IndexError: list index out of range

If this can help, here is the code in structlog that gets and uses “utcnow”:

        now_method = getattr(datetime.datetime, 'utcnow' if utc else 'now')
        if fmt is None:
            def stamper(self, _, __, event_dict):
                event_dict[key] = calendar.timegm(time.gmtime())
                return event_dict
        elif fmt.upper() == 'ISO':
            if utc:
                def stamper(self, _, __, event_dict):
                    event_dict[key] = now_method().isoformat() + 'Z'
                    return event_dict

[mindojo-victor]

Here is my attempt to fix this: https://github.com/spulec/freezegun/pull/155