# Django 2.2.9.dev20191202104323 文档

# django.utils.dateparse 源代码

    """Functions to parse datetime objects."""

    # We're using regular expressions rather than time.strptime because:
    # - They provide both validation and parsing.
    # - They're more flexible for datetimes.
    # - The date/datetime/time constructors produce friendlier error messages.

    import datetime
    import re

    from django.utils.timezone import get_fixed_timezone, utc

    date_re = re.compile(
        r'(?P<year>\d{4})-(?P<month>\d{1,2})-(?P<day>\d{1,2})$'
    )

    time_re = re.compile(
        r'(?P<hour>\d{1,2}):(?P<minute>\d{1,2})'
        r'(?::(?P<second>\d{1,2})(?:\.(?P<microsecond>\d{1,6})\d{0,6})?)?'
    )

    datetime_re = re.compile(
        r'(?P<year>\d{4})-(?P<month>\d{1,2})-(?P<day>\d{1,2})'
        r'[T ](?P<hour>\d{1,2}):(?P<minute>\d{1,2})'
        r'(?::(?P<second>\d{1,2})(?:\.(?P<microsecond>\d{1,6})\d{0,6})?)?'
        r'(?P<tzinfo>Z|[+-]\d{2}(?::?\d{2})?)?$'
    )

    standard_duration_re = re.compile(
        r'^'
        r'(?:(?P<days>-?\d+) (days?, )?)?'
        r'((?:(?P<hours>-?\d+):)(?=\d+:\d+))?'
        r'(?:(?P<minutes>-?\d+):)?'
        r'(?P<seconds>-?\d+)'
        r'(?:\.(?P<microseconds>\d{1,6})\d{0,6})?'
        r'$'
    )

    # Support the sections of ISO 8601 date representation that are accepted by
    # timedelta
    iso8601_duration_re = re.compile(
        r'^(?P<sign>[-+]?)'
        r'P'
        r'(?:(?P<days>\d+(.\d+)?)D)?'
        r'(?:T'
        r'(?:(?P<hours>\d+(.\d+)?)H)?'
        r'(?:(?P<minutes>\d+(.\d+)?)M)?'
        r'(?:(?P<seconds>\d+(.\d+)?)S)?'
        r')?'
        r'$'
    )

    # Support PostgreSQL's day-time interval format, e.g. "3 days 04:05:06". The
    # year-month and mixed intervals cannot be converted to a timedelta and thus
    # aren't accepted.
    postgres_interval_re = re.compile(
        r'^'
        r'(?:(?P<days>-?\d+) (days? ?))?'
        r'(?:(?P<sign>[-+])?'
        r'(?P<hours>\d+):'
        r'(?P<minutes>\d\d):'
        r'(?P<seconds>\d\d)'
        r'(?:\.(?P<microseconds>\d{1,6}))?'
        r')?$'
    )

    def parse_date(value):
        """Parse a string and return a datetime.date.

        Raise ValueError if the input is well formatted but not a valid date.
        Return None if the input isn't well formatted.
        """
        match = date_re.match(value)
        if match:
            kw = {k: int(v) for k, v in match.groupdict().items()}
            return datetime.date(**kw)

    def parse_time(value):
        """Parse a string and return a datetime.time.

        This function doesn't support time zone offsets.

        Raise ValueError if the input is well formatted but not a valid time.
        Return None if the input isn't well formatted, in particular if it
        contains an offset.
        """
        match = time_re.match(value)
        if match:
            kw = match.groupdict()
            kw['microsecond'] = kw['microsecond'] and kw['microsecond'].ljust(6, '0')
            kw = {k: int(v) for k, v in kw.items() if v is not None}
            return datetime.time(**kw)

    def parse_datetime(value):
        """Parse a string and return a datetime.datetime.

        This function supports time zone offsets. When the input contains one,
        the output uses a timezone with a fixed offset from UTC.

        Raise ValueError if the input is well formatted but not a valid datetime.
        Return None if the input isn't well formatted.
        """
        match = datetime_re.match(value)
        if match:
            kw = match.groupdict()
            kw['microsecond'] = kw['microsecond'] and kw['microsecond'].ljust(6, '0')
            tzinfo = kw.pop('tzinfo')
            if tzinfo == 'Z':
                tzinfo = utc
            elif tzinfo is not None:
                offset_mins = int(tzinfo[-2:]) if len(tzinfo) > 3 else 0
                offset = 60 * int(tzinfo[1:3]) + offset_mins
                if tzinfo[0] == '-':
                    offset = -offset
                tzinfo = get_fixed_timezone(offset)
            kw = {k: int(v) for k, v in kw.items() if v is not None}
            kw['tzinfo'] = tzinfo
            return datetime.datetime(**kw)

    def parse_duration(value):
        """Parse a duration string and return a datetime.timedelta.

        The preferred format for durations in Django is '%d %H:%M:%S.%f'.

        Also supports ISO 8601 representation and PostgreSQL's day-time interval
        format.
        """
        match = (
            standard_duration_re.match(value) or
            iso8601_duration_re.match(value) or
            postgres_interval_re.match(value)
        )
        if match:
            kw = match.groupdict()
            days = datetime.timedelta(float(kw.pop('days', 0) or 0))
            sign = -1 if kw.pop('sign', '+') == '-' else 1
            if kw.get('microseconds'):
                kw['microseconds'] = kw['microseconds'].ljust(6, '0')
            if kw.get('seconds') and kw.get('microseconds') and kw['seconds'].startswith('-'):
                kw['microseconds'] = '-' + kw['microseconds']
            kw = {k: float(v) for k, v in kw.items() if v is not None}
            return days + sign * datetime.timedelta(**kw)