420 lines
13 KiB
Python
420 lines
13 KiB
Python
from six import PY2
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from functools import wraps
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from datetime import datetime, timedelta, tzinfo
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ZERO = timedelta(0)
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__all__ = ['tzname_in_python2', 'enfold']
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def tzname_in_python2(namefunc):
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"""Change unicode output into bytestrings in Python 2
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tzname() API changed in Python 3. It used to return bytes, but was changed
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to unicode strings
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"""
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if PY2:
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@wraps(namefunc)
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def adjust_encoding(*args, **kwargs):
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name = namefunc(*args, **kwargs)
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if name is not None:
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name = name.encode()
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return name
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return adjust_encoding
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else:
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return namefunc
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# The following is adapted from Alexander Belopolsky's tz library
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# https://github.com/abalkin/tz
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if hasattr(datetime, 'fold'):
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# This is the pre-python 3.6 fold situation
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def enfold(dt, fold=1):
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"""
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Provides a unified interface for assigning the ``fold`` attribute to
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datetimes both before and after the implementation of PEP-495.
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:param fold:
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The value for the ``fold`` attribute in the returned datetime. This
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should be either 0 or 1.
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:return:
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Returns an object for which ``getattr(dt, 'fold', 0)`` returns
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``fold`` for all versions of Python. In versions prior to
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Python 3.6, this is a ``_DatetimeWithFold`` object, which is a
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subclass of :py:class:`datetime.datetime` with the ``fold``
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attribute added, if ``fold`` is 1.
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.. versionadded:: 2.6.0
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"""
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return dt.replace(fold=fold)
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else:
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class _DatetimeWithFold(datetime):
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"""
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This is a class designed to provide a PEP 495-compliant interface for
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Python versions before 3.6. It is used only for dates in a fold, so
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the ``fold`` attribute is fixed at ``1``.
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.. versionadded:: 2.6.0
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"""
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__slots__ = ()
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def replace(self, *args, **kwargs):
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"""
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Return a datetime with the same attributes, except for those
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attributes given new values by whichever keyword arguments are
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specified. Note that tzinfo=None can be specified to create a naive
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datetime from an aware datetime with no conversion of date and time
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data.
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This is reimplemented in ``_DatetimeWithFold`` because pypy3 will
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return a ``datetime.datetime`` even if ``fold`` is unchanged.
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"""
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argnames = (
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'year', 'month', 'day', 'hour', 'minute', 'second',
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'microsecond', 'tzinfo'
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)
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for arg, argname in zip(args, argnames):
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if argname in kwargs:
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raise TypeError('Duplicate argument: {}'.format(argname))
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kwargs[argname] = arg
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for argname in argnames:
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if argname not in kwargs:
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kwargs[argname] = getattr(self, argname)
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dt_class = self.__class__ if kwargs.get('fold', 1) else datetime
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return dt_class(**kwargs)
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@property
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def fold(self):
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return 1
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def enfold(dt, fold=1):
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"""
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Provides a unified interface for assigning the ``fold`` attribute to
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datetimes both before and after the implementation of PEP-495.
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:param fold:
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The value for the ``fold`` attribute in the returned datetime. This
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should be either 0 or 1.
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:return:
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Returns an object for which ``getattr(dt, 'fold', 0)`` returns
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``fold`` for all versions of Python. In versions prior to
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Python 3.6, this is a ``_DatetimeWithFold`` object, which is a
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subclass of :py:class:`datetime.datetime` with the ``fold``
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attribute added, if ``fold`` is 1.
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.. versionadded:: 2.6.0
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"""
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if getattr(dt, 'fold', 0) == fold:
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return dt
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args = dt.timetuple()[:6]
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args += (dt.microsecond, dt.tzinfo)
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if fold:
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return _DatetimeWithFold(*args)
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else:
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return datetime(*args)
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def _validate_fromutc_inputs(f):
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"""
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The CPython version of ``fromutc`` checks that the input is a ``datetime``
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object and that ``self`` is attached as its ``tzinfo``.
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"""
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@wraps(f)
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def fromutc(self, dt):
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if not isinstance(dt, datetime):
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raise TypeError("fromutc() requires a datetime argument")
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if dt.tzinfo is not self:
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raise ValueError("dt.tzinfo is not self")
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return f(self, dt)
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return fromutc
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class _tzinfo(tzinfo):
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"""
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Base class for all ``dateutil`` ``tzinfo`` objects.
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"""
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def is_ambiguous(self, dt):
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"""
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Whether or not the "wall time" of a given datetime is ambiguous in this
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zone.
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:param dt:
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A :py:class:`datetime.datetime`, naive or time zone aware.
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:return:
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Returns ``True`` if ambiguous, ``False`` otherwise.
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.. versionadded:: 2.6.0
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"""
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dt = dt.replace(tzinfo=self)
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wall_0 = enfold(dt, fold=0)
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wall_1 = enfold(dt, fold=1)
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same_offset = wall_0.utcoffset() == wall_1.utcoffset()
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same_dt = wall_0.replace(tzinfo=None) == wall_1.replace(tzinfo=None)
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return same_dt and not same_offset
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def _fold_status(self, dt_utc, dt_wall):
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"""
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Determine the fold status of a "wall" datetime, given a representation
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of the same datetime as a (naive) UTC datetime. This is calculated based
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on the assumption that ``dt.utcoffset() - dt.dst()`` is constant for all
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datetimes, and that this offset is the actual number of hours separating
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``dt_utc`` and ``dt_wall``.
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:param dt_utc:
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Representation of the datetime as UTC
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:param dt_wall:
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Representation of the datetime as "wall time". This parameter must
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either have a `fold` attribute or have a fold-naive
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:class:`datetime.tzinfo` attached, otherwise the calculation may
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fail.
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"""
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if self.is_ambiguous(dt_wall):
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delta_wall = dt_wall - dt_utc
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_fold = int(delta_wall == (dt_utc.utcoffset() - dt_utc.dst()))
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else:
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_fold = 0
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return _fold
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def _fold(self, dt):
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return getattr(dt, 'fold', 0)
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def _fromutc(self, dt):
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"""
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Given a timezone-aware datetime in a given timezone, calculates a
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timezone-aware datetime in a new timezone.
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Since this is the one time that we *know* we have an unambiguous
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datetime object, we take this opportunity to determine whether the
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datetime is ambiguous and in a "fold" state (e.g. if it's the first
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occurrence, chronologically, of the ambiguous datetime).
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:param dt:
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A timezone-aware :class:`datetime.datetime` object.
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"""
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# Re-implement the algorithm from Python's datetime.py
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dtoff = dt.utcoffset()
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if dtoff is None:
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raise ValueError("fromutc() requires a non-None utcoffset() "
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"result")
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# The original datetime.py code assumes that `dst()` defaults to
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# zero during ambiguous times. PEP 495 inverts this presumption, so
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# for pre-PEP 495 versions of python, we need to tweak the algorithm.
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dtdst = dt.dst()
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if dtdst is None:
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raise ValueError("fromutc() requires a non-None dst() result")
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delta = dtoff - dtdst
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dt += delta
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# Set fold=1 so we can default to being in the fold for
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# ambiguous dates.
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dtdst = enfold(dt, fold=1).dst()
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if dtdst is None:
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raise ValueError("fromutc(): dt.dst gave inconsistent "
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"results; cannot convert")
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return dt + dtdst
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@_validate_fromutc_inputs
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def fromutc(self, dt):
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"""
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Given a timezone-aware datetime in a given timezone, calculates a
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timezone-aware datetime in a new timezone.
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Since this is the one time that we *know* we have an unambiguous
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datetime object, we take this opportunity to determine whether the
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datetime is ambiguous and in a "fold" state (e.g. if it's the first
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occurrence, chronologically, of the ambiguous datetime).
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:param dt:
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A timezone-aware :class:`datetime.datetime` object.
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"""
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dt_wall = self._fromutc(dt)
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# Calculate the fold status given the two datetimes.
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_fold = self._fold_status(dt, dt_wall)
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# Set the default fold value for ambiguous dates
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return enfold(dt_wall, fold=_fold)
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class tzrangebase(_tzinfo):
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"""
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This is an abstract base class for time zones represented by an annual
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transition into and out of DST. Child classes should implement the following
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methods:
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* ``__init__(self, *args, **kwargs)``
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* ``transitions(self, year)`` - this is expected to return a tuple of
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datetimes representing the DST on and off transitions in standard
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time.
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A fully initialized ``tzrangebase`` subclass should also provide the
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following attributes:
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* ``hasdst``: Boolean whether or not the zone uses DST.
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* ``_dst_offset`` / ``_std_offset``: :class:`datetime.timedelta` objects
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representing the respective UTC offsets.
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* ``_dst_abbr`` / ``_std_abbr``: Strings representing the timezone short
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abbreviations in DST and STD, respectively.
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* ``_hasdst``: Whether or not the zone has DST.
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.. versionadded:: 2.6.0
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"""
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def __init__(self):
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raise NotImplementedError('tzrangebase is an abstract base class')
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def utcoffset(self, dt):
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isdst = self._isdst(dt)
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if isdst is None:
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return None
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elif isdst:
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return self._dst_offset
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else:
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return self._std_offset
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def dst(self, dt):
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isdst = self._isdst(dt)
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if isdst is None:
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return None
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elif isdst:
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return self._dst_base_offset
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else:
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return ZERO
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@tzname_in_python2
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def tzname(self, dt):
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if self._isdst(dt):
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return self._dst_abbr
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else:
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return self._std_abbr
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def fromutc(self, dt):
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""" Given a datetime in UTC, return local time """
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if not isinstance(dt, datetime):
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raise TypeError("fromutc() requires a datetime argument")
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if dt.tzinfo is not self:
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raise ValueError("dt.tzinfo is not self")
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# Get transitions - if there are none, fixed offset
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transitions = self.transitions(dt.year)
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if transitions is None:
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return dt + self.utcoffset(dt)
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# Get the transition times in UTC
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dston, dstoff = transitions
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dston -= self._std_offset
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dstoff -= self._std_offset
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utc_transitions = (dston, dstoff)
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dt_utc = dt.replace(tzinfo=None)
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isdst = self._naive_isdst(dt_utc, utc_transitions)
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if isdst:
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dt_wall = dt + self._dst_offset
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else:
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dt_wall = dt + self._std_offset
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_fold = int(not isdst and self.is_ambiguous(dt_wall))
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return enfold(dt_wall, fold=_fold)
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def is_ambiguous(self, dt):
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"""
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Whether or not the "wall time" of a given datetime is ambiguous in this
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zone.
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:param dt:
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A :py:class:`datetime.datetime`, naive or time zone aware.
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:return:
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Returns ``True`` if ambiguous, ``False`` otherwise.
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.. versionadded:: 2.6.0
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"""
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if not self.hasdst:
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return False
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start, end = self.transitions(dt.year)
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dt = dt.replace(tzinfo=None)
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return (end <= dt < end + self._dst_base_offset)
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def _isdst(self, dt):
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if not self.hasdst:
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return False
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elif dt is None:
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return None
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transitions = self.transitions(dt.year)
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if transitions is None:
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return False
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dt = dt.replace(tzinfo=None)
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isdst = self._naive_isdst(dt, transitions)
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# Handle ambiguous dates
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if not isdst and self.is_ambiguous(dt):
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return not self._fold(dt)
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else:
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return isdst
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def _naive_isdst(self, dt, transitions):
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dston, dstoff = transitions
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dt = dt.replace(tzinfo=None)
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if dston < dstoff:
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isdst = dston <= dt < dstoff
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else:
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isdst = not dstoff <= dt < dston
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return isdst
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@property
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def _dst_base_offset(self):
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return self._dst_offset - self._std_offset
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__hash__ = None
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def __ne__(self, other):
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return not (self == other)
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def __repr__(self):
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return "%s(...)" % self.__class__.__name__
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__reduce__ = object.__reduce__
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