#!/usr/bin/env python
'''$Id$'''
__rcs_id__ = '$Id$'
__version__ = '$Revision$'[11:-2]
from datetime import datetime, timedelta, tzinfo
from bisect import bisect_right
from sets import Set
_timedelta_cache = {}
def memorized_timedelta(seconds):
'''Create only one instance of each distinct timedelta'''
try:
return _timedelta_cache[seconds]
except KeyError:
delta = timedelta(seconds=seconds)
_timedelta_cache[seconds] = delta
return delta
_datetime_cache = {}
def memorized_datetime(*args):
'''Create only one instance of each distinct datetime'''
try:
return _datetime_cache[args]
except KeyError:
dt = datetime(*args)
_datetime_cache[args] = dt
return dt
_ttinfo_cache = {}
def memorized_ttinfo(*args):
'''Create only one instance of each distinct tuple'''
try:
return _ttinfo_cache[args]
except KeyError:
ttinfo = (
memorized_timedelta(args[0]),
memorized_timedelta(args[1]),
args[2]
)
_ttinfo_cache[args] = ttinfo
return ttinfo
_notime = memorized_timedelta(0)
class BaseTzInfo(tzinfo):
# Overridden in subclass
_utcoffset = None
_tzname = None
_zone = None
def __str__(self):
return self._zone
class StaticTzInfo(BaseTzInfo):
'''A timezone that has a constant offset from UTC
These timezones are rare, as most regions have changed their
offset from UTC at some point in their history
'''
def fromutc(self, dt):
'''See datetime.tzinfo.fromutc'''
return (dt + self._utcoffset).replace(tzinfo=self)
def utcoffset(self,dt):
'''See datetime.tzinfo.utcoffset'''
return self._utcoffset
def dst(self,dt):
'''See datetime.tzinfo.dst'''
return _notime
def tzname(self,dt):
'''See datetime.tzinfo.tzname'''
return self._tzname
def localize(self, dt, is_dst=False):
'''Convert naive time to local time'''
if dt.tzinfo is not None:
raise ValueError, 'Not naive datetime (tzinfo is already set)'
return dt.replace(tzinfo=self)
def normalize(self, dt, is_dst=False):
'''Correct the timezone information on the given datetime'''
if dt.tzinfo is None:
raise ValueError, 'Naive time - no tzinfo set'
return dt.replace(tzinfo=self)
def __repr__(self):
return '<StaticTzInfo %r>' % (self._zone,)
class DstTzInfo(BaseTzInfo):
'''A timezone that has a variable offset from UTC
The offset might change if daylight savings time comes into effect,
or at a point in history when the region decides to change their
timezone definition.
'''
# Overridden in subclass
_utc_transition_times = None # Sorted list of DST transition times in UTC
_transition_info = None # [(utcoffset, dstoffset, tzname)] corresponding
# to _utc_transition_times entries
_zone = None
# Set in __init__
_tzinfos = None
_dst = None # DST offset
def __init__(self, _inf=None, _tzinfos=None):
if _inf:
self._tzinfos = _tzinfos
self._utcoffset, self._dst, self._tzname = _inf
else:
_tzinfos = {}
self._tzinfos = _tzinfos
self._utcoffset, self._dst, self._tzname = self._transition_info[0]
_tzinfos[self._transition_info[0]] = self
for inf in self._transition_info[1:]:
if not _tzinfos.has_key(inf):
_tzinfos[inf] = self.__class__(inf, _tzinfos)
def fromutc(self, dt):
'''See datetime.tzinfo.fromutc'''
dt = dt.replace(tzinfo=None)
idx = max(0, bisect_right(self._utc_transition_times, dt) - 1)
inf = self._transition_info[idx]
return (dt + inf[0]).replace(tzinfo=self._tzinfos[inf])
def normalize(self, dt):
'''Correct the timezone information on the given datetime
If date arithmetic crosses DST boundaries, the tzinfo
is not magically adjusted. This method normalizes the
tzinfo to the correct one.
To test, first we need to do some setup
>>> from pytz import timezone
>>> utc = timezone('UTC')
>>> eastern = timezone('US/Eastern')
>>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
We next create a datetime right on an end-of-DST transition point,
the instant when the wallclocks are wound back one hour.
>>> utc_dt = datetime(2002, 10, 27, 6, 0, 0, tzinfo=utc)
>>> loc_dt = utc_dt.astimezone(eastern)
>>> loc_dt.strftime(fmt)
'2002-10-27 01:00:00 EST (-0500)'
Now, if we subtract a few minutes from it, note that the timezone
information has not changed.
>>> before = loc_dt - timedelta(minutes=10)
>>> before.strftime(fmt)
'2002-10-27 00:50:00 EST (-0500)'
But we can fix that by calling the normalize method
>>> before = eastern.normalize(before)
>>> before.strftime(fmt)
'2002-10-27 01:50:00 EDT (-0400)'
'''
if dt.tzinfo is None:
raise ValueError, 'Naive time - no tzinfo set'
# Convert dt in localtime to UTC
offset = dt.tzinfo._utcoffset
dt = dt.replace(tzinfo=None)
dt = dt - offset
# convert it back, and return it
return self.fromutc(dt)
def localize(self, dt, is_dst=False):
'''Convert naive time to local time.
This method should be used to construct localtimes, rather
than passing a tzinfo argument to a datetime constructor.
is_dst is used to determine the correct timezone in the ambigous
period at the end of daylight savings time.
>>> from pytz import timezone
>>> fmt = '%Y-%m-%d %H:%M:%S %Z (%z)'
>>> amdam = timezone('Europe/Amsterdam')
>>> dt = datetime(2004, 10, 31, 2, 0, 0)
>>> loc_dt1 = amdam.localize(dt, is_dst=True)
>>> loc_dt2 = amdam.localize(dt, is_dst=False)
>>> loc_dt1.strftime(fmt)
'2004-10-31 02:00:00 CEST (+0200)'
>>> loc_dt2.strftime(fmt)
'2004-10-31 02:00:00 CET (+0100)'
>>> str(loc_dt2 - loc_dt1)
'1:00:00'
Use is_dst=None to raise an AmbiguousTimeError for ambiguous
times at the end of daylight savings
>>> try:
... loc_dt1 = amdam.localize(dt, is_dst=None)
... except AmbiguousTimeError:
... print 'Oops'
Oops
>>> loc_dt1 = amdam.localize(dt, is_dst=None)
Traceback (most recent call last):
[...]
AmbiguousTimeError: 2004-10-31 02:00:00
is_dst defaults to False
>>> amdam.localize(dt) == amdam.localize(dt, False)
True
'''
if dt.tzinfo is not None:
raise ValueError, 'Not naive datetime (tzinfo is already set)'
# Find the possibly correct timezones. We probably just have one,
# but we might end up with two if we are in the end-of-DST
# transition period. Or possibly more in some particularly confused
# location...
possible_loc_dt = Set()
for tzinfo in self._tzinfos.values():
loc_dt = tzinfo.normalize(dt.replace(tzinfo=tzinfo))
if loc_dt.replace(tzinfo=None) == dt:
possible_loc_dt.add(loc_dt)
if len(possible_loc_dt) == 1:
return possible_loc_dt.pop()
# If told to be strict, raise an exception since we have an
# ambiguous case
if is_dst is None:
raise AmbiguousTimeError(dt)
# Filter out the possiblilities that don't match the requested
# is_dst
filtered_possible_loc_dt = [
p for p in possible_loc_dt
if bool(p.tzinfo._dst) == is_dst
]
# Hopefully we only have one possibility left. Return it.
if len(filtered_possible_loc_dt) == 1:
return filtered_possible_loc_dt[0]
if len(filtered_possible_loc_dt) == 0:
filtered_possible_loc_dt = list(possible_loc_dt)
# If we get this far, we have in a wierd timezone transition
# where the clocks have been wound back but is_dst is the same
# in both (eg. Europe/Warsaw 1915 when they switched to CET).
# At this point, we just have to guess unless we allow more
# hints to be passed in (such as the UTC offset or abbreviation),
# but that is just getting silly.
#
# Choose the earliest (by UTC) applicable timezone.
def mycmp(a,b):
return cmp(
a.replace(tzinfo=None) - a.tzinfo._utcoffset,
b.replace(tzinfo=None) - b.tzinfo._utcoffset,
)
filtered_possible_loc_dt.sort(mycmp)
return filtered_possible_loc_dt[0]
def utcoffset(self, dt):
'''See datetime.tzinfo.utcoffset'''
return self._utcoffset
def dst(self, dt):
'''See datetime.tzinfo.dst'''
return self._dst
def tzname(self, dt):
'''See datetime.tzinfo.tzname'''
return self._tzname
def __repr__(self):
if self._dst:
dst = 'DST'
else:
dst = 'STD'
if self._utcoffset > _notime:
return '<DstTzInfo %r %s+%s %s>' % (
self._zone, self._tzname, self._utcoffset, dst
)
else:
return '<DstTzInfo %r %s%s %s>' % (
self._zone, self._tzname, self._utcoffset, dst
)
class AmbiguousTimeError(Exception):
'''Exception raised when attempting to create an ambiguous wallclock time.
At the end of a DST transition period, a particular wallclock time will
occur twice (once before the clocks are set back, once after). Both
possibilities may be correct, unless further information is supplied.
See DstTzInfo.normalize() for more info
'''
