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