# documentación de Django - 1.10.7

# Código fuente para django.utils.dateparse

    """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 import six
    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'
        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'$'
    )

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

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

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

        This function doesn't support time zone offsets.

        Raises ValueError if the input is well formatted but not a valid time.
        Returns 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()
            if kw['microsecond']:
                kw['microsecond'] = kw['microsecond'].ljust(6, '0')
            kw = {k: int(v) for k, v in six.iteritems(kw) if v is not None}
            return datetime.time(**kw)

    def parse_datetime(value):
        """Parses 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.

        Raises ValueError if the input is well formatted but not a valid datetime.
        Returns None if the input isn't well formatted.
        """
        match = datetime_re.match(value)
        if match:
            kw = match.groupdict()
            if kw['microsecond']:
                kw['microsecond'] = 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 six.iteritems(kw) if v is not None}
            kw['tzinfo'] = tzinfo
            return datetime.datetime(**kw)

    def parse_duration(value):
        """Parses a duration string and returns a datetime.timedelta.

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

        Also supports ISO 8601 representation.
        """
        match = standard_duration_re.match(value)
        if not match:
            match = iso8601_duration_re.match(value)
        if match:
            kw = match.groupdict()
            if kw.get('microseconds'):
                kw['microseconds'] = kw['microseconds'].ljust(6, '0')
            kw = {k: float(v) for k, v in six.iteritems(kw) if v is not None}
            return datetime.timedelta(**kw)