379 lines
10 KiB
Python
379 lines
10 KiB
Python
"""
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Timezone-related classes and 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 sys
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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 django.utils import six
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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 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 FixedOffset(tzinfo):
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"""
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Fixed offset in minutes east from UTC. Taken from Python's docs.
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Kept as close as possible to the reference version. __init__ was changed
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to make its arguments optional, according to Python's requirement that
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tzinfo subclasses can be instantiated without arguments.
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"""
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def __init__(self, offset=None, name=None):
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if offset is not None:
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self.__offset = timedelta(minutes=offset)
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if name is not None:
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self.__name = name
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def utcoffset(self, dt):
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return self.__offset
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def tzname(self, dt):
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return self.__name
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def dst(self, dt):
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return ZERO
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class ReferenceLocalTimezone(tzinfo):
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"""
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Local time. 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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Kept as close as possible to the reference version. __init__ was added to
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delay the computation of STDOFFSET, DSTOFFSET and DSTDIFF which is
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performed at import time in the example.
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Subclasses contain further improvements.
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"""
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def __init__(self):
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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 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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class LocalTimezone(ReferenceLocalTimezone):
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"""
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Slightly improved local time implementation focusing on correctness.
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It still crashes on dates before 1970 or after 2038, but at least the
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error message is helpful.
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"""
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def tzname(self, dt):
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is_dst = False if dt is None else self._isdst(dt)
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return _time.tzname[is_dst]
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def _isdst(self, dt):
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try:
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return super(LocalTimezone, self)._isdst(dt)
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except (OverflowError, ValueError) as exc:
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exc_type = type(exc)
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exc_value = exc_type(
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"Unsupported value: %r. You should install pytz." % dt)
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exc_value.__cause__ = exc
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six.reraise(exc_type, exc_value, sys.exc_info()[2])
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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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def get_fixed_timezone(offset):
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"""
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Returns a tzinfo instance with a fixed offset from UTC.
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"""
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if isinstance(offset, timedelta):
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offset = offset.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 FixedOffset(offset, name)
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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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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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This is the time zone defined by settings.TIME_ZONE.
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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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# This relies on os.environ['TZ'] being set to settings.TIME_ZONE.
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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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return timezone.tzname(None)
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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 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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Checks 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 = (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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# If `value` is naive, astimezone() will raise a ValueError,
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# so we don't need to perform a redundant check.
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value = value.astimezone(timezone)
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if hasattr(timezone, 'normalize'):
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# This method is 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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# This method is 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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# 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):
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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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# If `value` is naive, astimezone() will raise a ValueError,
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# so we don't need to perform a redundant check.
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value = value.astimezone(timezone)
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if hasattr(timezone, 'normalize'):
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# This method is 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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