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# -*- coding: utf-8 -*-
# Copyright (c) 2014, Brandon Nielsen
# All rights reserved.
#
# This software may be modified and distributed under the terms
# of the BSD license. See the LICENSE file for details.
import datetime
from aniso8601.resolution import DateResolution
def get_date_resolution(isodatestr):
#Valid string formats are:
#
#Y[YYY]
#YYYY-MM-DD
#YYYYMMDD
#YYYY-MM
#YYYY-Www
#YYYYWww
#YYYY-Www-D
#YYYYWwwD
#YYYY-DDD
#YYYYDDD
if isodatestr.startswith('+') or isodatestr.startswith('-'):
raise NotImplementedError('ISO8601 extended year representation not supported.')
isodatestrlen = len(isodatestr)
if isodatestr.find('W') != -1:
#Handle ISO8601 week date format
hyphens_present = 1 if isodatestr.find('-') != -1 else 0
week_date_len = 7 + hyphens_present
weekday_date_len = 8 + 2*hyphens_present
if isodatestrlen == week_date_len:
#YYYY-Www
#YYYYWww
return DateResolution.Week
elif isodatestrlen == weekday_date_len:
#YYYY-Www-D
#YYYYWwwD
return DateResolution.Weekday
else:
raise ValueError('String is not a valid ISO8601 week date.')
#If the size of the string of 4 or less, assume its a truncated year representation
if len(isodatestr) <= 4:
return DateResolution.Year
#An ISO string may be a calendar represntation if:
# 1) When split on a hyphen, the sizes of the parts are 4, 2, 2 or 4, 2
# 2) There are no hyphens, and the length is 8
datestrsplit = isodatestr.split('-')
#Check case 1
if len(datestrsplit) == 2:
if len(datestrsplit[0]) == 4 and len(datestrsplit[1]) == 2:
return DateResolution.Month
if len(datestrsplit) == 3:
if len(datestrsplit[0]) == 4 and len(datestrsplit[1]) == 2 and len(datestrsplit[2]) == 2:
return DateResolution.Day
#Check case 2
if len(isodatestr) == 8 and isodatestr.find('-') == -1:
return DateResolution.Day
#An ISO string may be a ordinal date representation if:
# 1) When split on a hyphen, the sizes of the parts are 4, 3
# 2) There are no hyphens, and the length is 7
#Check case 1
if len(datestrsplit) == 2:
if len(datestrsplit[0]) == 4 and len(datestrsplit[1]) == 3:
return DateResolution.Ordinal
#Check case 2
if len(isodatestr) == 7 and isodatestr.find('-') == -1:
return DateResolution.Ordinal
#None of the date representations match
raise ValueError('String is not an ISO8601 date, perhaps it represents a time or datetime.')
def parse_date(isodatestr):
#Given a string in any ISO8601 date format, return a datetime.date
#object that corresponds to the given date. Valid string formats are:
#
#Y[YYY]
#YYYY-MM-DD
#YYYYMMDD
#YYYY-MM
#YYYY-Www
#YYYYWww
#YYYY-Www-D
#YYYYWwwD
#YYYY-DDD
#YYYYDDD
#
#Note that the ISO8601 date format of ±YYYYY is expressly not supported
return _resolution_map[get_date_resolution(isodatestr)](isodatestr)
def _parse_year(yearstr):
#yearstr is of the format Y[YYY]
#
#0000 (1 BC) is not representible as a Python date so a ValueError is
#raised
#
#Truncated dates, like '19', refer to 1900-1999 inclusive, we simply parse
#to 1900-01-01
#
#Since no additional resolution is provided, the month is set to 1, and
#day is set to 1
if len(yearstr) == 4:
return datetime.date(int(yearstr), 1, 1)
else:
#Shift 0s in from the left to form complete year
return datetime.date(int(yearstr.ljust(4, '0')), 1, 1)
def _parse_calendar_day(datestr):
#datestr is of the format YYYY-MM-DD or YYYYMMDD
datestrlen = len(datestr)
if datestrlen == 10:
#YYYY-MM-DD
strformat = '%Y-%m-%d'
elif datestrlen == 8:
#YYYYMMDD
strformat = '%Y%m%d'
else:
raise ValueError('String is not a valid ISO8601 calendar day.')
parseddatetime = datetime.datetime.strptime(datestr, strformat)
#Since no 'time' is given, cast to a date
return parseddatetime.date()
def _parse_calendar_month(datestr):
#datestr is of the format YYYY-MM
datestrlen = len(datestr)
if datestrlen != 7:
raise ValueError('String is not a valid ISO8601 calendar month.')
parseddatetime = datetime.datetime.strptime(datestr, '%Y-%m')
#Since no 'time' is given, cast to a date
return parseddatetime.date()
def _parse_week_day(datestr):
#datestr is of the format YYYY-Www-D, YYYYWwwD
#
#W is the week number prefix, ww is the week number, between 1 and 53
#0 is not a valid week number, which differs from the Python implementation
#
#D is the weekday number, between 1 and 7, which differs from the Python
#implementation which is between 0 and 6
isoyear = int(datestr[0:4])
gregorianyearstart = _iso_year_start(isoyear)
#Week number will be the two characters after the W
windex = datestr.find('W')
isoweeknumber = int(datestr[windex + 1:windex + 3])
if isoweeknumber == 0:
raise ValueError('00 is not a valid ISO8601 weeknumber.')
datestrlen = len(datestr)
if datestr.find('-') != -1:
if datestrlen == 10:
#YYYY-Www-D
isoday = int(datestr[9:10])
return gregorianyearstart + datetime.timedelta(weeks=isoweeknumber - 1, days=isoday - 1)
else:
raise ValueError('String is not a valid ISO8601 week date.')
else:
if datestrlen == 8:
#YYYYWwwD
isoday = int(datestr[7:8])
return gregorianyearstart + datetime.timedelta(weeks=isoweeknumber - 1, days=isoday - 1)
else:
raise ValueError('String is not a valid ISO8601 week date.')
def _parse_week(datestr):
#datestr is of the format YYYY-Www, YYYYWww
#
#W is the week number prefix, ww is the week number, between 1 and 53
#0 is not a valid week number, which differs from the Python implementation
isoyear = int(datestr[0:4])
gregorianyearstart = _iso_year_start(isoyear)
#Week number will be the two characters after the W
windex = datestr.find('W')
isoweeknumber = int(datestr[windex + 1:windex + 3])
if isoweeknumber == 0:
raise ValueError('00 is not a valid ISO8601 weeknumber.')
datestrlen = len(datestr)
if datestr.find('-') != -1:
if datestrlen == 8:
#YYYY-Www
#Suss out the date
return gregorianyearstart + datetime.timedelta(weeks=isoweeknumber - 1, days=0)
else:
raise ValueError('String is not a valid ISO8601 week date.')
else:
if datestrlen == 7:
#YYYYWww
return gregorianyearstart + datetime.timedelta(weeks=isoweeknumber - 1, days=0)
else:
raise ValueError('String is not a valid ISO8601 week date.')
def _parse_ordinal_date(datestr):
#datestr is of the format YYYY-DDD or YYYYDDD
#DDD can be from 1 - 365, this matches Python's definition
if datestr.find('-') != -1:
#YYYY-DDD
parseddatetime = datetime.datetime.strptime(datestr, '%Y-%j')
#Since no 'time' is given, cast to a date
return parseddatetime.date()
else:
#YYYYDDD
parseddatetime = datetime.datetime.strptime(datestr, '%Y%j')
#Since no 'time' is given, cast to a date
return parseddatetime.date()
def _iso_year_start(isoyear):
#Given an ISO year, returns the equivalent of the start of the year on the
#Gregorian calendar (which is used by Python)
#Stolen from:
#http://stackoverflow.com/questions/304256/whats-the-best-way-to-find-the-inverse-of-datetime-isocalendar
#Determine the location of the 4th of January, the first week of the ISO
#year in the week containing the 4th of January
#http://en.wikipedia.org/wiki/ISO_week_date
fourth_jan = datetime.date(isoyear, 1, 4)
#Note the conversion from ISO day (1 - 7) and Python day (0 - 6)
delta = datetime.timedelta(fourth_jan.isoweekday() - 1)
#Return the start of the year
return fourth_jan - delta
_resolution_map = {
DateResolution.Day: _parse_calendar_day,
DateResolution.Ordinal: _parse_ordinal_date,
DateResolution.Month: _parse_calendar_month,
DateResolution.Week: _parse_week,
DateResolution.Weekday: _parse_week_day,
DateResolution.Year: _parse_year
}
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