""" 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.isoerror import ISO8601Error from isodate.isostrf import DATE_EXT_COMPLETE, strftime 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 def add_re(regex_text): cache_entry.append(re.compile(r"\A" + regex_text + r"\Z")) # 1. complete dates: # YYYY-MM-DD or +- YYYYYY-MM-DD... extended date format add_re( r"(?P[+-]){%d}(?P[0-9]{%d})" r"-(?P[0-9]{2})-(?P[0-9]{2})" % (sign, yeardigits) ) # YYYYMMDD or +- YYYYYYMMDD... basic date format add_re( r"(?P[+-]){%d}(?P[0-9]{%d})" r"(?P[0-9]{2})(?P[0-9]{2})" % (sign, yeardigits) ) # 2. complete week dates: # YYYY-Www-D or +-YYYYYY-Www-D ... extended week date add_re( r"(?P[+-]){%d}(?P[0-9]{%d})" r"-W(?P[0-9]{2})-(?P[0-9]{1})" % (sign, yeardigits) ) # YYYYWwwD or +-YYYYYYWwwD ... basic week date add_re( r"(?P[+-]){%d}(?P[0-9]{%d})W" r"(?P[0-9]{2})(?P[0-9]{1})" % (sign, yeardigits) ) # 3. ordinal dates: # YYYY-DDD or +-YYYYYY-DDD ... extended format add_re( r"(?P[+-]){%d}(?P[0-9]{%d})" r"-(?P[0-9]{3})" % (sign, yeardigits) ) # YYYYDDD or +-YYYYYYDDD ... basic format add_re( r"(?P[+-]){%d}(?P[0-9]{%d})" r"(?P[0-9]{3})" % (sign, yeardigits) ) # 4. week dates: # YYYY-Www or +-YYYYYY-Www ... extended reduced accuracy week date # 4. week dates: # YYYY-Www or +-YYYYYY-Www ... extended reduced accuracy week date add_re( r"(?P[+-]){%d}(?P[0-9]{%d})" r"-W(?P[0-9]{2})" % (sign, yeardigits) ) # YYYYWww or +-YYYYYYWww ... basic reduced accuracy week date add_re( r"(?P[+-]){%d}(?P[0-9]{%d})W" r"(?P[0-9]{2})" % (sign, yeardigits) ) # 5. month dates: # YYY-MM or +-YYYYYY-MM ... reduced accuracy specific month # 5. month dates: # YYY-MM or +-YYYYYY-MM ... reduced accuracy specific month add_re( r"(?P[+-]){%d}(?P[0-9]{%d})" r"-(?P[0-9]{2})" % (sign, yeardigits) ) # YYYMM or +-YYYYYYMM ... basic incomplete month date format add_re( r"(?P[+-]){%d}(?P[0-9]{%d})" r"(?P[0-9]{2})" % (sign, yeardigits) ) # 6. year dates: # YYYY or +-YYYYYY ... reduced accuracy specific year add_re(r"(?P[+-]){%d}(?P[0-9]{%d})" % (sign, yeardigits)) # 7. century dates: # YY or +-YYYY ... reduced accuracy specific century add_re(r"(?P[+-]){%d}" r"(?P[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, defaultmonth=1, defaultday=1): """ 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 YYYMM +-YYYYYYMM basic incomplete month 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), defaultmonth, defaultday ) 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.replace(month=defaultmonth, day=defaultday) # year-, month-, or complete date if "day" not in groups or groups["day"] is None: day = defaultday else: day = int(groups["day"]) return date( sign * int(groups["year"]), int(groups["month"]) or defaultmonth, 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)