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from six import PY3
from functools import wraps
from datetime import datetime, timedelta, tzinfo
ZERO = timedelta(0)
__all__ = ['tzname_in_python2', 'enfold']
def tzname_in_python2(namefunc):
"""Change unicode output into bytestrings in Python 2
tzname() API changed in Python 3. It used to return bytes, but was changed
to unicode strings
"""
def adjust_encoding(*args, **kwargs):
name = namefunc(*args, **kwargs)
if name is not None and not PY3:
name = name.encode()
return name
return adjust_encoding
# The following is adapted from Alexander Belopolsky's tz library
# https://github.com/abalkin/tz
if hasattr(datetime, 'fold'):
# This is the pre-python 3.6 fold situation
def enfold(dt, fold=1):
"""
Provides a unified interface for assigning the ``fold`` attribute to
datetimes both before and after the implementation of PEP-495.
:param fold:
The value for the ``fold`` attribute in the returned datetime. This
should be either 0 or 1.
:return:
Returns an object for which ``getattr(dt, 'fold', 0)`` returns
``fold`` for all versions of Python. In versions prior to
Python 3.6, this is a ``_DatetimeWithFold`` object, which is a
subclass of :py:class:`datetime.datetime` with the ``fold``
attribute added, if ``fold`` is 1.
.. versionadded:: 2.6.0
"""
return dt.replace(fold=fold)
else:
class _DatetimeWithFold(datetime):
"""
This is a class designed to provide a PEP 495-compliant interface for
Python versions before 3.6. It is used only for dates in a fold, so
the ``fold`` attribute is fixed at ``1``.
.. versionadded:: 2.6.0
"""
__slots__ = ()
@property
def fold(self):
return 1
def enfold(dt, fold=1):
"""
Provides a unified interface for assigning the ``fold`` attribute to
datetimes both before and after the implementation of PEP-495.
:param fold:
The value for the ``fold`` attribute in the returned datetime. This
should be either 0 or 1.
:return:
Returns an object for which ``getattr(dt, 'fold', 0)`` returns
``fold`` for all versions of Python. In versions prior to
Python 3.6, this is a ``_DatetimeWithFold`` object, which is a
subclass of :py:class:`datetime.datetime` with the ``fold``
attribute added, if ``fold`` is 1.
.. versionadded:: 2.6.0
"""
if getattr(dt, 'fold', 0) == fold:
return dt
args = dt.timetuple()[:6]
args += (dt.microsecond, dt.tzinfo)
if fold:
return _DatetimeWithFold(*args)
else:
return datetime(*args)
def _validate_fromutc_inputs(f):
"""
The CPython version of ``fromutc`` checks that the input is a ``datetime``
object and that ``self`` is attached as its ``tzinfo``.
"""
@wraps(f)
def fromutc(self, dt):
if not isinstance(dt, datetime):
raise TypeError("fromutc() requires a datetime argument")
if dt.tzinfo is not self:
raise ValueError("dt.tzinfo is not self")
return f(self, dt)
return fromutc
class _tzinfo(tzinfo):
"""
Base class for all ``dateutil`` ``tzinfo`` objects.
"""
def is_ambiguous(self, dt):
"""
Whether or not the "wall time" of a given datetime is ambiguous in this
zone.
:param dt:
A :py:class:`datetime.datetime`, naive or time zone aware.
:return:
Returns ``True`` if ambiguous, ``False`` otherwise.
.. versionadded:: 2.6.0
"""
dt = dt.replace(tzinfo=self)
wall_0 = enfold(dt, fold=0)
wall_1 = enfold(dt, fold=1)
same_offset = wall_0.utcoffset() == wall_1.utcoffset()
same_dt = wall_0.replace(tzinfo=None) == wall_1.replace(tzinfo=None)
return same_dt and not same_offset
def _fold_status(self, dt_utc, dt_wall):
"""
Determine the fold status of a "wall" datetime, given a representation
of the same datetime as a (naive) UTC datetime. This is calculated based
on the assumption that ``dt.utcoffset() - dt.dst()`` is constant for all
datetimes, and that this offset is the actual number of hours separating
``dt_utc`` and ``dt_wall``.
:param dt_utc:
Representation of the datetime as UTC
:param dt_wall:
Representation of the datetime as "wall time". This parameter must
either have a `fold` attribute or have a fold-naive
:class:`datetime.tzinfo` attached, otherwise the calculation may
fail.
"""
if self.is_ambiguous(dt_wall):
delta_wall = dt_wall - dt_utc
_fold = int(delta_wall == (dt_utc.utcoffset() - dt_utc.dst()))
else:
_fold = 0
return _fold
def _fold(self, dt):
return getattr(dt, 'fold', 0)
def _fromutc(self, dt):
"""
Given a timezone-aware datetime in a given timezone, calculates a
timezone-aware datetime in a new timezone.
Since this is the one time that we *know* we have an unambiguous
datetime object, we take this opportunity to determine whether the
datetime is ambiguous and in a "fold" state (e.g. if it's the first
occurence, chronologically, of the ambiguous datetime).
:param dt:
A timezone-aware :class:`datetime.datetime` object.
"""
# Re-implement the algorithm from Python's datetime.py
dtoff = dt.utcoffset()
if dtoff is None:
raise ValueError("fromutc() requires a non-None utcoffset() "
"result")
# The original datetime.py code assumes that `dst()` defaults to
# zero during ambiguous times. PEP 495 inverts this presumption, so
# for pre-PEP 495 versions of python, we need to tweak the algorithm.
dtdst = dt.dst()
if dtdst is None:
raise ValueError("fromutc() requires a non-None dst() result")
delta = dtoff - dtdst
dt += delta
# Set fold=1 so we can default to being in the fold for
# ambiguous dates.
dtdst = enfold(dt, fold=1).dst()
if dtdst is None:
raise ValueError("fromutc(): dt.dst gave inconsistent "
"results; cannot convert")
return dt + dtdst
@_validate_fromutc_inputs
def fromutc(self, dt):
"""
Given a timezone-aware datetime in a given timezone, calculates a
timezone-aware datetime in a new timezone.
Since this is the one time that we *know* we have an unambiguous
datetime object, we take this opportunity to determine whether the
datetime is ambiguous and in a "fold" state (e.g. if it's the first
occurance, chronologically, of the ambiguous datetime).
:param dt:
A timezone-aware :class:`datetime.datetime` object.
"""
dt_wall = self._fromutc(dt)
# Calculate the fold status given the two datetimes.
_fold = self._fold_status(dt, dt_wall)
# Set the default fold value for ambiguous dates
return enfold(dt_wall, fold=_fold)
class tzrangebase(_tzinfo):
"""
This is an abstract base class for time zones represented by an annual
transition into and out of DST. Child classes should implement the following
methods:
* ``__init__(self, *args, **kwargs)``
* ``transitions(self, year)`` - this is expected to return a tuple of
datetimes representing the DST on and off transitions in standard
time.
A fully initialized ``tzrangebase`` subclass should also provide the
following attributes:
* ``hasdst``: Boolean whether or not the zone uses DST.
* ``_dst_offset`` / ``_std_offset``: :class:`datetime.timedelta` objects
representing the respective UTC offsets.
* ``_dst_abbr`` / ``_std_abbr``: Strings representing the timezone short
abbreviations in DST and STD, respectively.
* ``_hasdst``: Whether or not the zone has DST.
.. versionadded:: 2.6.0
"""
def __init__(self):
raise NotImplementedError('tzrangebase is an abstract base class')
def utcoffset(self, dt):
isdst = self._isdst(dt)
if isdst is None:
return None
elif isdst:
return self._dst_offset
else:
return self._std_offset
def dst(self, dt):
isdst = self._isdst(dt)
if isdst is None:
return None
elif isdst:
return self._dst_base_offset
else:
return ZERO
@tzname_in_python2
def tzname(self, dt):
if self._isdst(dt):
return self._dst_abbr
else:
return self._std_abbr
def fromutc(self, dt):
""" Given a datetime in UTC, return local time """
if not isinstance(dt, datetime):
raise TypeError("fromutc() requires a datetime argument")
if dt.tzinfo is not self:
raise ValueError("dt.tzinfo is not self")
# Get transitions - if there are none, fixed offset
transitions = self.transitions(dt.year)
if transitions is None:
return dt + self.utcoffset(dt)
# Get the transition times in UTC
dston, dstoff = transitions
dston -= self._std_offset
dstoff -= self._std_offset
utc_transitions = (dston, dstoff)
dt_utc = dt.replace(tzinfo=None)
isdst = self._naive_isdst(dt_utc, utc_transitions)
if isdst:
dt_wall = dt + self._dst_offset
else:
dt_wall = dt + self._std_offset
_fold = int(not isdst and self.is_ambiguous(dt_wall))
return enfold(dt_wall, fold=_fold)
def is_ambiguous(self, dt):
"""
Whether or not the "wall time" of a given datetime is ambiguous in this
zone.
:param dt:
A :py:class:`datetime.datetime`, naive or time zone aware.
:return:
Returns ``True`` if ambiguous, ``False`` otherwise.
.. versionadded:: 2.6.0
"""
if not self.hasdst:
return False
start, end = self.transitions(dt.year)
dt = dt.replace(tzinfo=None)
return (end <= dt < end + self._dst_base_offset)
def _isdst(self, dt):
if not self.hasdst:
return False
elif dt is None:
return None
transitions = self.transitions(dt.year)
if transitions is None:
return False
dt = dt.replace(tzinfo=None)
isdst = self._naive_isdst(dt, transitions)
# Handle ambiguous dates
if not isdst and self.is_ambiguous(dt):
return not self._fold(dt)
else:
return isdst
def _naive_isdst(self, dt, transitions):
dston, dstoff = transitions
dt = dt.replace(tzinfo=None)
if dston < dstoff:
isdst = dston <= dt < dstoff
else:
isdst = not dstoff <= dt < dston
return isdst
@property
def _dst_base_offset(self):
return self._dst_offset - self._std_offset
__hash__ = None
def __ne__(self, other):
return not (self == other)
def __repr__(self):
return "%s(...)" % self.__class__.__name__
__reduce__ = object.__reduce__
def _total_seconds(td):
# Python 2.6 doesn't have a total_seconds() method on timedelta objects
return ((td.seconds + td.days * 86400) * 1000000 +
td.microseconds) // 1000000
_total_seconds = getattr(timedelta, 'total_seconds', _total_seconds)
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