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Diffstat (limited to 'python/dateutil/tz/_common.py')
| -rw-r--r-- | python/dateutil/tz/_common.py | 394 |
1 files changed, 394 insertions, 0 deletions
diff --git a/python/dateutil/tz/_common.py b/python/dateutil/tz/_common.py new file mode 100644 index 0000000..f1cf2af --- /dev/null +++ b/python/dateutil/tz/_common.py @@ -0,0 +1,394 @@ +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) |