""" Convert COARDS time specification to a datetime object. """ from datetime import datetime, timedelta import re import warnings EPOCH = datetime(1970, 1, 1) # constants in seconds SECOND = 1.0 MINUTE = 60.0 HOUR = 3.6e3 DAY = 8.64e4 SHAKE = 1e-8 SIDEREAL_DAY = 8.616409e4 SIDEREAL_HOUR = 3.590170e3 SIDEREAL_MINUTE = 5.983617e1 SIDEREAL_SECOND = 0.9972696 SIDEREAL_YEAR = 3.155815e7 TROPICAL_YEAR = 3.15569259747e7 LUNAR_MONTH = 29.530589 * DAY COMMON_YEAR = 365 * DAY LEAP_YEAR = 366 * DAY JULIAN_YEAR = 365.25 * DAY GREGORIAN_YEAR = 365.2425 * DAY SIDEREAL_MONTH = 27.321661 * DAY TROPICAL_MONTH = 27.321582 * DAY FORTNIGHT = 14 * DAY WEEK = 7 * DAY JIFFY = 1e-2 EON = 1e9 * TROPICAL_YEAR MONTH = TROPICAL_YEAR/12 MILLISECOND = 1e-3 MICROSECOND = 1e-6 class ParserError(Exception): pass class Parser(object): def __init__(self, units): parts = units.split(' since ') self.units = parse_units(parts[0]) self.offset = parse_date(parts[1]) def __call__(self, value): seconds = value*self.units try: date = EPOCH + timedelta(seconds=self.offset+seconds) except OverflowError: warnings.warn( "Shifted data 366 days to the future, since year zero does not exist.", UserWarning) date = EPOCH + timedelta(seconds=self.offset+seconds+LEAP_YEAR) return date class Formatter(object): def __init__(self, units): parts = units.split(' since ') self.units = parse_units(parts[0]) self.offset = parse_date(parts[1]) def __call__(self, date): dt = (date - EPOCH) value = dt.days*DAY + dt.seconds + dt.microseconds*MICROSECOND - self.offset return value / self.units class Converter(object): def __init__(self, from_, to): self.parser = Parser(from_) self.formatter = Formatter(to) def __call__(self, value): return self.formatter(self.parser(value)) def parse(value, units): """ Parse a COARDS compliant date:: >>> parse(0, "hours since 1970-01-01 00:00:00") datetime.datetime(1970, 1, 1, 0, 0) >>> parse(0, "hours since 1970-01-01 00:00:00 +2:30") datetime.datetime(1969, 12, 31, 21, 30) >>> parse(10, "hours since 1996-1-1") datetime.datetime(1996, 1, 1, 10, 0) >>> parse(10, "hours since 1-1-1") datetime.datetime(1, 1, 1, 10, 0) >>> parse(10, "hours since 1990-11-25 12:00:00") datetime.datetime(1990, 11, 25, 22, 0) >>> parse(10, "hours since 1990-11-25 12:00") datetime.datetime(1990, 11, 25, 22, 0) >>> parse(10, "hours since 1990-11-25 12:00 +2:00") datetime.datetime(1990, 11, 25, 20, 0) >>> parse(10, "hours since 1990-11-25 12:00 UTC") datetime.datetime(1990, 11, 25, 22, 0) >>> parse(10, "seconds since 1970-1-1") datetime.datetime(1970, 1, 1, 0, 0, 10) It works with a year that never existed, since it's usual to have the origin set to the year zero in climatological datasets:: >>> parse(366, "days since 0000-01-01 00:00:00") datetime.datetime(1, 1, 1, 0, 0) """ parser = Parser(units) return parser(value) def format(date, units): """ Convert a datetime object into a COARDS compliant date:: >>> print(format(datetime(1970, 1, 1, 0, 0), "hours since 1970-01-01 00:00:00")) 0.0 >>> print(format(datetime(1969, 12, 31, 21, 30), "hours since 1970-01-01 00:00:00 +2:30")) 0.0 >>> print(format(datetime(1996, 1, 1, 10, 0), "hours since 1996-1-1")) 10.0 >>> print(format(datetime(1, 1, 1, 10, 0), "hours since 1-1-1")) 10.0 >>> print(format(datetime(1990, 11, 25, 22, 0), "hours since 1990-11-25 12:00:00")) 10.0 >>> print(format(datetime(1990, 11, 25, 22, 0), "hours since 1990-11-25 12:00")) 10.0 >>> print(format(datetime(1990, 11, 25, 20, 0), "hours since 1990-11-25 12:00 +2:00")) 10.0 >>> print(format(datetime(1990, 11, 25, 22, 0), "hours since 1990-11-25 12:00 UTC")) 10.0 >>> print(format(datetime(1970, 1, 1, 0, 0, 10), "seconds since 1970-1-1")) 10.0 It works with a year that never existed, since it's usual to have the origin set to the year zero in climatological datasets:: >>> print(format(datetime(1, 1, 1, 0, 0), "days since 0000-01-01 00:00:00")) 366.0 """ formatter = Formatter(units) return formatter(date) def parse_units(units): """ Parse units. This function transforms all Udunits defined time units, returning it converted to seconds:: >>> print(parse_units("min")) 60.0 """ udunits = [(SECOND, ['second', 'seconds', 'sec', 's', 'secs']), (MINUTE, ['minute', 'minutes', 'min']), (HOUR, ['hour', 'hours', 'hr', 'h']), (DAY, ['day', 'days', 'd']), (SHAKE, ['shake', 'shakes']), (SIDEREAL_DAY, ['sidereal_day', 'sidereal_days']), (SIDEREAL_HOUR, ['sidereal_hour', 'sidereal_hours']), (SIDEREAL_MINUTE, ['sidereal_minute', 'sidereal_minutes']), (SIDEREAL_SECOND, ['sidereal_second', 'sidereal_seconds']), (SIDEREAL_YEAR, ['sidereal_year', 'sidereal_years']), (TROPICAL_YEAR, ['tropical_year', 'tropical_years', 'year', 'years', 'yr', 'a']), (LUNAR_MONTH, ['lunar_month', 'lunar_months']), (COMMON_YEAR, ['common_year', 'common_years']), (LEAP_YEAR, ['leap_year', 'leap_years']), (JULIAN_YEAR, ['julian_year', 'julian_years']), (GREGORIAN_YEAR, ['gregorian_year', 'gregorian_years']), (SIDEREAL_MONTH, ['sidereal_month', 'sidereal_months']), (TROPICAL_MONTH, ['tropical_month', 'tropical_months']), (FORTNIGHT, ['fortnight', 'fortnights']), (WEEK, ['week', 'weeks']), (JIFFY, ['jiffy', 'jiffies']), (EON, ['eon', 'eons']), (MONTH, ['month', 'months']), (MILLISECOND, ['msec', 'msecs']), (MICROSECOND, ['usec', 'usecs', 'microsecond', 'microseconds']), ] for seconds, valid in udunits: if units in valid: return seconds raise ParserError('Invalid date units: %s' % units) def parse_date(date): """ Parses a date string and returns number of seconds from the EPOCH. """ # yyyy-mm-dd [hh:mm:ss[.s][ [+-]hh[:][mm]]] p = re.compile( r'''(?P\d{1,4}) # yyyy - # (?P\d{1,2}) # mm or m - # (?P\d{1,2}) # dd or d # (?: # [optional time and timezone] (?:\s|T) # (?P\d{1,2}) # hh or h :? # (?P\d{1,2})? # mm or m (?: # [optional seconds] : # (?P\d{1,2}) # ss or s # (?: # [optional decisecond] \. # . (?P\d) # s )? # )? # (?: # [optional timezone] \s? # ((?: # (?P[+-]? # [+ or -] \d{1,2}) # hh or h :? # [:] (?P\d{2})? # [mm] ) # | # or (?:UTC)|(?:Z)) # UTC | Z )? # )? # $ # EOL ''', re.VERBOSE) m = p.match(date) if m: c = m.groupdict(0) for k, v in c.items(): c[k] = int(v) # get timezone offset in seconds tz_offset = c['ho']*HOUR + c['mo']*MINUTE # Some datasets use the date "0000-01-01 00:00:00" as an origin, even though # the year zero does not exist in the Gregorian/Julian calendars. if c['year'] == 0: c['year'] = 1 year_offset = LEAP_YEAR else: year_offset = 0 origin = datetime(c['year'], c['month'], c['day'], c['hour'], c['min'], c['sec'], c['dsec'] * 100000) dt = origin - EPOCH return dt.days*DAY + dt.seconds + dt.microseconds*MICROSECOND - year_offset - tz_offset raise ParserError('Invalid date: %s' % date) from_udunits = parse to_udunits = format def _test(): import doctest doctest.testmod() if __name__ == "__main__": _test()