DateTimeField enforce_timezone() cannot handle DST information

[alxnik]

We have a web API with USE_TZ enabled which receives naive datetimes. In the last change of DST, the API started responding HTTP 400 errors for values between 03:00 and 04:00 (local) due to pytz raising AmbiguousTimeError.

Although this is somewhat expected behaviour, if the client doesn't have the DST information (and if the client sends naive datetime then most probably it doesn't have this information), there is no way to receive these values.

2 proposed solutions would be to:

1. The DatetimeField could have a default_dst parameter (true/false) if pytz raises AmbiguousTimeError (this assumes that at least SOME loss of information will happen)
2. Allow for a callback function that will do the conversion in the user code

We have worked around the issue by sublcassing & overriding enforce_timezone() as below and then doing custom conversion in the validate_() of the serializer.

class NonEnforcingDateTimeField(serializers.DateTimeField):
    def enforce_timezone(self, value):
        return value

Although our solution works perfectly fine, this seems like a generic enough issue to warrant some kind of handling logic in DRF, or maybe a warning in the documentation.