Reversing the result of Django's naturaltime

Question

Django's humanize module is fantastic for turning datetime objects into something that makes more sense to us as humans with it's naturaltime function (docs). What I'm trying to do is the reverse, taking any one of the naturaltime formats and converting it back to a datetime (accepting the obvious loss of precision).

Is there any existing library to do this or am I going to have to write my own datetime.strptime patterns?

I know this is a bit of a "find me a tool/library" question, but I've googled around quite a bit with no results.

Answer 1

For any future searchers, I ended up writing dehumanize to handle this question. It's on github here.

from datetime import datetime, timedelta
import re


def naturaltime(text, now=None):
    """Convert a django naturaltime string to a datetime object."""
    if not now:
        now = datetime.now()

    if text == 'now':
        return now
    if "ago" in text:
        multiplier = -1
    elif "from now" in text:
        multiplier = 1
    else:
        raise ValueError("%s is not a valid naturaltime" % text)

    text = text.replace('an ', '1 ')
    text = text.replace('a ', '1 ')

    days = get_first(r'(\d*) day', text)
    hours = get_first(r'(\d*) hour', text)
    minutes = get_first(r'(\d*) minute', text)
    seconds = get_first(r'(\d*) second', text)
    delta = timedelta(days=days, hours=hours, minutes=minutes, seconds=seconds)
    delta *= multiplier
    return now + delta


def get_first(pattern, text):
    """Return either a matched number or 0."""
    matches = re.findall(pattern, text)
    if matches:
        return int(matches[0])
    else:
        return 0