forked from varia/varia.website
293 lines
8.3 KiB
Python
293 lines
8.3 KiB
Python
"""Timezone helper functions.
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This module uses pytz when it's available and fallbacks when it isn't.
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"""
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from datetime import datetime, timedelta, tzinfo
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from threading import local
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import time as _time
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try:
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import pytz
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except ImportError:
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pytz = None
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# ### from django.conf import settings
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from . import six
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__all__ = [
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'utc', 'get_default_timezone', 'get_current_timezone',
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'activate', 'deactivate', 'override',
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'is_naive', 'is_aware', 'make_aware', 'make_naive',
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]
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# UTC and local time zones
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ZERO = timedelta(0)
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class UTC(tzinfo):
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"""
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UTC implementation taken from Python's docs.
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Used only when pytz isn't available.
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"""
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def __repr__(self):
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return "<UTC>"
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def utcoffset(self, dt):
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return ZERO
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def tzname(self, dt):
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return "UTC"
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def dst(self, dt):
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return ZERO
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class LocalTimezone(tzinfo):
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"""
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Local time implementation taken from Python's docs.
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Used only when pytz isn't available, and most likely inaccurate. If you're
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having trouble with this class, don't waste your time, just install pytz.
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"""
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def __init__(self):
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# This code is moved in __init__ to execute it as late as possible
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# See get_default_timezone().
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self.STDOFFSET = timedelta(seconds=-_time.timezone)
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if _time.daylight:
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self.DSTOFFSET = timedelta(seconds=-_time.altzone)
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else:
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self.DSTOFFSET = self.STDOFFSET
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self.DSTDIFF = self.DSTOFFSET - self.STDOFFSET
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tzinfo.__init__(self)
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def __repr__(self):
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return "<LocalTimezone>"
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def utcoffset(self, dt):
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if self._isdst(dt):
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return self.DSTOFFSET
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else:
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return self.STDOFFSET
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def dst(self, dt):
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if self._isdst(dt):
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return self.DSTDIFF
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else:
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return ZERO
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def tzname(self, dt):
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return _time.tzname[self._isdst(dt)]
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def _isdst(self, dt):
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tt = (dt.year, dt.month, dt.day,
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dt.hour, dt.minute, dt.second,
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dt.weekday(), 0, 0)
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stamp = _time.mktime(tt)
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tt = _time.localtime(stamp)
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return tt.tm_isdst > 0
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utc = pytz.utc if pytz else UTC()
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"""UTC time zone as a tzinfo instance."""
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# ### # In order to avoid accessing the settings at compile time,
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# ### # wrap the expression in a function and cache the result.
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# ### _localtime = None
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# ###
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# ### def get_default_timezone():
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# ### """
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# ### Returns the default time zone as a tzinfo instance.
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# ###
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# ### This is the time zone defined by settings.TIME_ZONE.
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# ###
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# ### See also :func:`get_current_timezone`.
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# ### """
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# ### global _localtime
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# ### if _localtime is None:
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# ### if isinstance(settings.TIME_ZONE, six.string_types) and pytz is not None:
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# ### _localtime = pytz.timezone(settings.TIME_ZONE)
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# ### else:
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# ### _localtime = LocalTimezone()
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# ### return _localtime
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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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"""
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Returns the name of the default time zone.
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"""
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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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"""
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Returns the currently active time zone as a tzinfo instance.
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"""
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return getattr(_active, "value", get_default_timezone())
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def get_current_timezone_name():
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"""
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Returns the name of the currently active time zone.
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"""
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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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Returns the name of ``timezone``.
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"""
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try:
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# for pytz timezones
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return timezone.zone
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except AttributeError:
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# for regular tzinfo objects
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local_now = datetime.now(timezone)
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return timezone.tzname(local_now)
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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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Sets 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. If it is a time zone name, pytz is required.
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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, six.string_types) and pytz is not None:
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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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Unsets 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(object):
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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 is it a time zone name, pytz is required.
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If it is ``None``, Django enables the default 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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self.old_timezone = getattr(_active, 'value', None)
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def __enter__(self):
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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 not None:
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_active.value = self.old_timezone
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else:
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del _active.value
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# ### # Templates
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# ###
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# ### def template_localtime(value, use_tz=None):
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# ### """
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# ### Checks if value is a datetime and converts it to local time if necessary.
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# ###
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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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# ###
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# ### This function is designed for use by the template engine.
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# ### """
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# ### should_convert = (isinstance(value, datetime)
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# ### and (settings.USE_TZ if use_tz is None else use_tz)
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# ### and not is_naive(value)
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# ### and getattr(value, 'convert_to_local_time', True))
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# ### return localtime(value) if should_convert else value
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# Utilities
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def localtime(value, timezone=None):
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"""
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Converts an aware datetime.datetime to local time.
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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 timezone is None:
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timezone = get_current_timezone()
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value = value.astimezone(timezone)
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if hasattr(timezone, 'normalize'):
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# available for pytz time zones
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value = timezone.normalize(value)
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return value
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# ### def now():
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# ### """
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# ### Returns an aware or naive datetime.datetime, depending on settings.USE_TZ.
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# ### """
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# ### if settings.USE_TZ:
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# ### # timeit shows that datetime.now(tz=utc) is 24% slower
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# ### return datetime.utcnow().replace(tzinfo=utc)
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# ### else:
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# ### return datetime.now()
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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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Determines if a given datetime.datetime is aware.
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The logic is described in Python's docs:
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http://docs.python.org/library/datetime.html#datetime.tzinfo
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"""
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return value.tzinfo is not None and value.tzinfo.utcoffset(value) is not None
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def is_naive(value):
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"""
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Determines if a given datetime.datetime is naive.
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The logic is described in Python's docs:
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http://docs.python.org/library/datetime.html#datetime.tzinfo
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"""
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return value.tzinfo is None or value.tzinfo.utcoffset(value) is None
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def make_aware(value, timezone):
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"""
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Makes a naive datetime.datetime in a given time zone aware.
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"""
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if hasattr(timezone, 'localize'):
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# available for pytz time zones
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return timezone.localize(value, is_dst=None)
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else:
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# may be wrong around DST changes
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return value.replace(tzinfo=timezone)
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def make_naive(value, timezone):
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"""
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Makes an aware datetime.datetime naive in a given time zone.
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"""
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value = value.astimezone(timezone)
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if hasattr(timezone, 'normalize'):
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# available for pytz time zones
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value = timezone.normalize(value)
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return value.replace(tzinfo=None)
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