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##############################################################################
# Copyright 2009, Gerhard Weis
# All rights reserved.
#
# Redistribution and use in source and binary forms, with or without
# modification, are permitted provided that the following conditions are met:
#
# * Redistributions of source code must retain the above copyright notice,
# this list of conditions and the following disclaimer.
# * Redistributions in binary form must reproduce the above copyright notice,
# this list of conditions and the following disclaimer in the documentation
# and/or other materials provided with the distribution.
# * Neither the name of the authors nor the names of its contributors
# may be used to endorse or promote products derived from this software
# without specific prior written permission.
#
# THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
# AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
# IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
# ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE
# LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
# CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
# SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
# INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
# CONTRACT, STRICT LIABILITY, OR TORT
##############################################################################
'''
This modules provides a method to parse an ISO 8601:2004 date string to a
python datetime.date instance.
It supports all basic, extended and expanded formats as described in the ISO
standard. The only limitations it has, are given by the Python datetime.date
implementation, which does not support dates before 0001-01-01.
'''
import re
from datetime import date, timedelta
from isodate.isostrf import strftime, DATE_EXT_COMPLETE
from isodate.isoerror import ISO8601Error
DATE_REGEX_CACHE = {}
# A dictionary to cache pre-compiled regular expressions.
# A set of regular expressions is identified, by number of year digits allowed
# and whether a plus/minus sign is required or not. (This option is changeable
# only for 4 digit years).
def build_date_regexps(yeardigits=4, expanded=False):
'''
Compile set of regular expressions to parse ISO dates. The expressions will
be created only if they are not already in REGEX_CACHE.
It is necessary to fix the number of year digits, else it is not possible
to automatically distinguish between various ISO date formats.
ISO 8601 allows more than 4 digit years, on prior agreement, but then a +/-
sign is required (expanded format). To support +/- sign for 4 digit years,
the expanded parameter needs to be set to True.
'''
if yeardigits != 4:
expanded = True
if (yeardigits, expanded) not in DATE_REGEX_CACHE:
cache_entry = []
# ISO 8601 expanded DATE formats allow an arbitrary number of year
# digits with a leading +/- sign.
if expanded:
sign = 1
else:
sign = 0
# 1. complete dates:
# YYYY-MM-DD or +- YYYYYY-MM-DD... extended date format
cache_entry.append(re.compile(r"(?P<sign>[+-]){%d}(?P<year>[0-9]{%d})"
r"-(?P<month>[0-9]{2})-(?P<day>[0-9]{2})"
% (sign, yeardigits)))
# YYYYMMDD or +- YYYYYYMMDD... basic date format
cache_entry.append(re.compile(r"(?P<sign>[+-]){%d}(?P<year>[0-9]{%d})"
r"(?P<month>[0-9]{2})(?P<day>[0-9]{2})"
% (sign, yeardigits)))
# 2. complete week dates:
# YYYY-Www-D or +-YYYYYY-Www-D ... extended week date
cache_entry.append(re.compile(r"(?P<sign>[+-]){%d}(?P<year>[0-9]{%d})"
r"-W(?P<week>[0-9]{2})-(?P<day>[0-9]{1})"
% (sign, yeardigits)))
# YYYYWwwD or +-YYYYYYWwwD ... basic week date
cache_entry.append(re.compile(r"(?P<sign>[+-]){%d}(?P<year>[0-9]{%d})W"
r"(?P<week>[0-9]{2})(?P<day>[0-9]{1})"
% (sign, yeardigits)))
# 3. ordinal dates:
# YYYY-DDD or +-YYYYYY-DDD ... extended format
cache_entry.append(re.compile(r"(?P<sign>[+-]){%d}(?P<year>[0-9]{%d})"
r"-(?P<day>[0-9]{3})"
% (sign, yeardigits)))
# YYYYDDD or +-YYYYYYDDD ... basic format
cache_entry.append(re.compile(r"(?P<sign>[+-]){%d}(?P<year>[0-9]{%d})"
r"(?P<day>[0-9]{3})"
% (sign, yeardigits)))
# 4. week dates:
# YYYY-Www or +-YYYYYY-Www ... extended reduced accuracy week date
cache_entry.append(re.compile(r"(?P<sign>[+-]){%d}(?P<year>[0-9]{%d})"
r"-W(?P<week>[0-9]{2})"
% (sign, yeardigits)))
# YYYYWww or +-YYYYYYWww ... basic reduced accuracy week date
cache_entry.append(re.compile(r"(?P<sign>[+-]){%d}(?P<year>[0-9]{%d})W"
r"(?P<week>[0-9]{2})"
% (sign, yeardigits)))
# 5. month dates:
# YYY-MM or +-YYYYYY-MM ... reduced accuracy specific month
cache_entry.append(re.compile(r"(?P<sign>[+-]){%d}(?P<year>[0-9]{%d})"
r"-(?P<month>[0-9]{2})"
% (sign, yeardigits)))
# 6. year dates:
# YYYY or +-YYYYYY ... reduced accuracy specific year
cache_entry.append(re.compile(r"(?P<sign>[+-]){%d}(?P<year>[0-9]{%d})"
% (sign, yeardigits)))
# 7. century dates:
# YY or +-YYYY ... reduced accuracy specific century
cache_entry.append(re.compile(r"(?P<sign>[+-]){%d}"
r"(?P<century>[0-9]{%d})"
% (sign, yeardigits - 2)))
DATE_REGEX_CACHE[(yeardigits, expanded)] = cache_entry
return DATE_REGEX_CACHE[(yeardigits, expanded)]
def parse_date(datestring, yeardigits=4, expanded=False):
'''
Parse an ISO 8601 date string into a datetime.date object.
As the datetime.date implementation is limited to dates starting from
0001-01-01, negative dates (BC) and year 0 can not be parsed by this
method.
For incomplete dates, this method chooses the first day for it. For
instance if only a century is given, this method returns the 1st of
January in year 1 of this century.
supported formats: (expanded formats are shown with 6 digits for year)
YYYYMMDD +-YYYYYYMMDD basic complete date
YYYY-MM-DD +-YYYYYY-MM-DD extended complete date
YYYYWwwD +-YYYYYYWwwD basic complete week date
YYYY-Www-D +-YYYYYY-Www-D extended complete week date
YYYYDDD +-YYYYYYDDD basic ordinal date
YYYY-DDD +-YYYYYY-DDD extended ordinal date
YYYYWww +-YYYYYYWww basic incomplete week date
YYYY-Www +-YYYYYY-Www extended incomplete week date
YYY-MM +-YYYYYY-MM incomplete month date
YYYY +-YYYYYY incomplete year date
YY +-YYYY incomplete century date
@param datestring: the ISO date string to parse
@param yeardigits: how many digits are used to represent a year
@param expanded: if True then +/- signs are allowed. This parameter
is forced to True, if yeardigits != 4
@return: a datetime.date instance represented by datestring
@raise ISO8601Error: if this function can not parse the datestring
@raise ValueError: if datestring can not be represented by datetime.date
'''
if yeardigits != 4:
expanded = True
isodates = build_date_regexps(yeardigits, expanded)
for pattern in isodates:
match = pattern.match(datestring)
if match:
groups = match.groupdict()
# sign, century, year, month, week, day,
# FIXME: negative dates not possible with python standard types
sign = (groups['sign'] == '-' and -1) or 1
if 'century' in groups:
return date(sign * (int(groups['century']) * 100 + 1), 1, 1)
if 'month' not in groups: # weekdate or ordinal date
ret = date(sign * int(groups['year']), 1, 1)
if 'week' in groups:
isotuple = ret.isocalendar()
if 'day' in groups:
days = int(groups['day'] or 1)
else:
days = 1
# if first week in year, do weeks-1
return ret + timedelta(weeks=int(groups['week']) -
(((isotuple[1] == 1) and 1) or 0),
days=-isotuple[2] + days)
elif 'day' in groups: # ordinal date
return ret + timedelta(days=int(groups['day'])-1)
else: # year date
return ret
# year-, month-, or complete date
if 'day' not in groups or groups['day'] is None:
day = 1
else:
day = int(groups['day'])
return date(sign * int(groups['year']),
int(groups['month']) or 1, day)
raise ISO8601Error('Unrecognised ISO 8601 date format: %r' % datestring)
def date_isoformat(tdate, format=DATE_EXT_COMPLETE, yeardigits=4):
'''
Format date strings.
This method is just a wrapper around isodate.isostrf.strftime and uses
Date-Extended-Complete as default format.
'''
return strftime(tdate, format, yeardigits)
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