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# Date/time manipulation
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import datetime
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import dateutil.tz
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import strings
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import time
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utc = dateutil.tz.tzutc()
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local = dateutil.tz.tzlocal()
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def naive2utc(datetime_):
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    assert datetime_.tzinfo == None
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    return datetime_.replace(tzinfo=utc)
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def aware2local(datetime_): return datetime_.astimezone(local)
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def from_timestamp(utc_timestamp):
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    return naive2utc(datetime.datetime.utcfromtimestamp(utc_timestamp))
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def timestamp(datetime_):
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    datetime_ = aware2local(datetime_)
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    return int(time.mktime(datetime_.timetuple())) + datetime_.microsecond/1e6
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epoch = from_timestamp(0)
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def total_seconds(timedelta_): return timestamp(epoch + timedelta_)
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def now(): return datetime.datetime.now(utc)
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def strftime(format, datetime_):
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    '''datetime.strftime() can't handle years before 1900'''
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    return (datetime_.replace(year=epoch.year, day=1).strftime(format
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        .replace('%Y', '%%Y')
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        .replace('%d', '%%d')
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        )
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        .replace('%Y', '%04d' % datetime_.year)
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        .replace('%d', '%02d' % datetime_.day)
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        )
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def strtotime(str_, default=epoch):
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    import dateutil.parser
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    return dateutil.parser.parse(str_, default=default)
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def could_be_year(str_): return str_.isdigit() and len(str_) == 4
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def could_be_day(str_): return str_.isdigit() and len(str_) <= 2
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def parse_date_range(str_, range_sep='-', part_sep=' '):
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    default = (str_, None)
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    # range_sep might be used as date part separator instead
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    if str_.find(part_sep) < 0: return default
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    start, sep, end = str_.partition(range_sep)
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    if sep == '': return default # not a range
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    start, end = (strings.single_space(d).split(part_sep) for d in (start, end))
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    # Has form M D1-D2 or M D1-D2 Y (not M1 Y1-M2 Y2 or M1 D1-M2 D2)
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    if len(start) == 2 and (len(end) == 1 or (
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            len(end) == 2 and could_be_day(start[-1]) and could_be_day(end[0])
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            and could_be_year(end[-1])
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        )):
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        end.insert(0, start[0]) # make end fully specified
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    ct_diff = len(end) - len(start)
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    # Has form D1-D2 M Y, M1 D1-M2 D2 Y, M1-M2 Y, etc.
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    if ct_diff > 0: start += end[-ct_diff:] # make start fully specified
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    # Other forms are invalid and will be left as-is
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    return tuple(part_sep.join(d) for d in (start, end))
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