273 lines
7.9 KiB
Python
273 lines
7.9 KiB
Python
"""
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Timezone-related classes and functions.
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"""
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import functools
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from contextlib import ContextDecorator
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from datetime import datetime, timedelta, timezone, tzinfo
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import pytz
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from asgiref.local import Local
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from django.conf import settings
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__all__ = [
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'utc', 'get_fixed_timezone',
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'get_default_timezone', 'get_default_timezone_name',
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'get_current_timezone', 'get_current_timezone_name',
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'activate', 'deactivate', 'override',
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'localtime', 'now',
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'is_aware', 'is_naive', 'make_aware', 'make_naive',
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]
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# UTC time zone as a tzinfo instance.
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utc = pytz.utc
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_PYTZ_BASE_CLASSES = (pytz.tzinfo.BaseTzInfo, pytz._FixedOffset)
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# In releases prior to 2018.4, pytz.UTC was not a subclass of BaseTzInfo
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if not isinstance(pytz.UTC, pytz._FixedOffset):
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_PYTZ_BASE_CLASSES = _PYTZ_BASE_CLASSES + (type(pytz.UTC),)
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def get_fixed_timezone(offset):
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"""Return a tzinfo instance with a fixed offset from UTC."""
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if isinstance(offset, timedelta):
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offset = offset.total_seconds() // 60
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sign = '-' if offset < 0 else '+'
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hhmm = '%02d%02d' % divmod(abs(offset), 60)
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name = sign + hhmm
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return timezone(timedelta(minutes=offset), name)
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# In order to avoid accessing settings at compile time,
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# wrap the logic in a function and cache the result.
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@functools.lru_cache()
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def get_default_timezone():
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"""
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Return the default time zone as a tzinfo instance.
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This is the time zone defined by settings.TIME_ZONE.
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"""
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return pytz.timezone(settings.TIME_ZONE)
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# This function exists for consistency with get_current_timezone_name
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def get_default_timezone_name():
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"""Return the name of the default time zone."""
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return _get_timezone_name(get_default_timezone())
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_active = Local()
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def get_current_timezone():
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"""Return the currently active time zone as a tzinfo instance."""
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return getattr(_active, "value", get_default_timezone())
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def get_current_timezone_name():
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"""Return the name of the currently active time zone."""
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return _get_timezone_name(get_current_timezone())
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def _get_timezone_name(timezone):
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"""
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Return the offset for fixed offset timezones, or the name of timezone if
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not set.
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"""
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return timezone.tzname(None) or str(timezone)
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# Timezone selection functions.
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# These functions don't change os.environ['TZ'] and call time.tzset()
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# because it isn't thread safe.
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def activate(timezone):
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"""
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Set the time zone for the current thread.
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The ``timezone`` argument must be an instance of a tzinfo subclass or a
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time zone name.
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"""
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if isinstance(timezone, tzinfo):
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_active.value = timezone
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elif isinstance(timezone, str):
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_active.value = pytz.timezone(timezone)
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else:
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raise ValueError("Invalid timezone: %r" % timezone)
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def deactivate():
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"""
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Unset the time zone for the current thread.
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Django will then use the time zone defined by settings.TIME_ZONE.
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"""
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if hasattr(_active, "value"):
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del _active.value
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class override(ContextDecorator):
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"""
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Temporarily set the time zone for the current thread.
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This is a context manager that uses django.utils.timezone.activate()
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to set the timezone on entry and restores the previously active timezone
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on exit.
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The ``timezone`` argument must be an instance of a ``tzinfo`` subclass, a
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time zone name, or ``None``. If it is ``None``, Django enables the default
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time zone.
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"""
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def __init__(self, timezone):
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self.timezone = timezone
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def __enter__(self):
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self.old_timezone = getattr(_active, 'value', None)
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if self.timezone is None:
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deactivate()
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else:
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activate(self.timezone)
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def __exit__(self, exc_type, exc_value, traceback):
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if self.old_timezone is None:
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deactivate()
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else:
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_active.value = self.old_timezone
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# Templates
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def template_localtime(value, use_tz=None):
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"""
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Check if value is a datetime and converts it to local time if necessary.
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If use_tz is provided and is not None, that will force the value to
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be converted (or not), overriding the value of settings.USE_TZ.
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This function is designed for use by the template engine.
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"""
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should_convert = (
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isinstance(value, datetime) and
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(settings.USE_TZ if use_tz is None else use_tz) and
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not is_naive(value) and
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getattr(value, 'convert_to_local_time', True)
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)
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return localtime(value) if should_convert else value
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# Utilities
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def localtime(value=None, timezone=None):
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"""
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Convert an aware datetime.datetime to local time.
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Only aware datetimes are allowed. When value is omitted, it defaults to
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now().
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Local time is defined by the current time zone, unless another time zone
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is specified.
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"""
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if value is None:
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value = now()
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if timezone is None:
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timezone = get_current_timezone()
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# Emulate the behavior of astimezone() on Python < 3.6.
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if is_naive(value):
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raise ValueError("localtime() cannot be applied to a naive datetime")
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return value.astimezone(timezone)
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def localdate(value=None, timezone=None):
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"""
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Convert an aware datetime to local time and return the value's date.
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Only aware datetimes are allowed. When value is omitted, it defaults to
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now().
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Local time is defined by the current time zone, unless another time zone is
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specified.
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"""
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return localtime(value, timezone).date()
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def now():
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"""
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Return an aware or naive datetime.datetime, depending on settings.USE_TZ.
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"""
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return datetime.now(tz=utc if settings.USE_TZ else None)
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# By design, these four functions don't perform any checks on their arguments.
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# The caller should ensure that they don't receive an invalid value like None.
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def is_aware(value):
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"""
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Determine if a given datetime.datetime is aware.
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The concept is defined in Python's docs:
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https://docs.python.org/library/datetime.html#datetime.tzinfo
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Assuming value.tzinfo is either None or a proper datetime.tzinfo,
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value.utcoffset() implements the appropriate logic.
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"""
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return value.utcoffset() is not None
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def is_naive(value):
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"""
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Determine if a given datetime.datetime is naive.
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The concept is defined in Python's docs:
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https://docs.python.org/library/datetime.html#datetime.tzinfo
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Assuming value.tzinfo is either None or a proper datetime.tzinfo,
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value.utcoffset() implements the appropriate logic.
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"""
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return value.utcoffset() is None
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def make_aware(value, timezone=None, is_dst=None):
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"""Make a naive datetime.datetime in a given time zone aware."""
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if timezone is None:
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timezone = get_current_timezone()
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if _is_pytz_zone(timezone):
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# This method is available for pytz time zones.
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return timezone.localize(value, is_dst=is_dst)
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else:
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# Check that we won't overwrite the timezone of an aware datetime.
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if is_aware(value):
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raise ValueError(
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"make_aware expects a naive datetime, got %s" % value)
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# This may be wrong around DST changes!
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return value.replace(tzinfo=timezone)
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def make_naive(value, timezone=None):
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"""Make an aware datetime.datetime naive in a given time zone."""
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if timezone is None:
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timezone = get_current_timezone()
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# Emulate the behavior of astimezone() on Python < 3.6.
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if is_naive(value):
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raise ValueError("make_naive() cannot be applied to a naive datetime")
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return value.astimezone(timezone).replace(tzinfo=None)
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def _is_pytz_zone(tz):
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"""Checks if a zone is a pytz zone."""
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return isinstance(tz, _PYTZ_BASE_CLASSES)
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def _datetime_ambiguous_or_imaginary(dt, tz):
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if _is_pytz_zone(tz):
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try:
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tz.utcoffset(dt)
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except (pytz.AmbiguousTimeError, pytz.NonExistentTimeError):
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return True
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else:
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return False
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return tz.utcoffset(dt.replace(fold=not dt.fold)) != tz.utcoffset(dt)
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