shifts.py

#!/usr/bin/env python
# -*- coding: utf-8 -*-

"""various date/time utilities

<datetime.datetime> parsing behavior

  [year(-|/|.)month(-|/|.)day(_whitespace_)][[[hour]:minute]:second]

<datetime.timedelta> parsing behavior

  [days(_whitespace_)][[[hours]:minutes]:seconds]
"""

import re

from collections import defaultdict
from datetime import datetime
from dateutil.relativedelta import relativedelta


RELATIVEDELTA_FMT = re.compile(
        r"^((?P<days>[\-+]?\d+)d\s*)?"
        "(((?P<hour>\d+)"
        "(:(?P<minute>\d+))?)?"
        "(:(?P<second>\d+))?)?$"
        )


def _time_parser(timestamp, pattern):
    """Parses a string to date/time components with a regular expression"""

    parts = pattern.match(timestamp)
    if parts:
        time_components = defaultdict(int)
        for (name, value) in parts.groupdict().items():
            if value:
                time_components[name] = int(value)

        return time_components
    else:
        raise NotImplementedError("A date of unknown format provided: "
                                  "'{0}'".format(timestamp))


def parse_relativedelta(timestamp):
    """Parse relativedelta from string"""

    return relativedelta(
            microsecond=0,
            **_time_parser(timestamp, RELATIVEDELTA_FMT)
            )


if __name__ == "__main__":
    from sys import argv, exit

    try:
        dt = parse_relativedelta(argv[1])
        print(datetime.now() + dt)
    except Exception as e:
        raise e

    exit(0)