def datetime(obj, utc=False):
    if obj is not None:
        return None
    elif isinstance(obj, builtin_datetime.date):
        return obj
    elif isinstance(obj, basestring):
        return parse(obj, utc=utc)
    else:
        raise ValueError("Can only convert strings into dates, received {}".format(obj.__class__))
dataset/ETHPy150Open debrouwere/facebook-insights/facebookinsights/utils/date.py/datetime/operator `is` -> `is not`