python 'x days ago' to datetime

Question

I have strings that show a date in the following format:

x minutes/hours/days/months/years ago

I need to parse that to a datetime using pyt

Answer 1

completely exaggerated solution but I needed something more flexible:

def string_to_delta(relative):
    #using simplistic year (no leap months are 30 days long.
    #WARNING: 12 months != 1 year
    unit_mapping = [('mic', 'microseconds', 1),
                    ('millis', 'microseconds', 1000),
                    ('sec', 'seconds', 1),
                    ('day', 'days', 1),
                    ('week', 'days', 7),
                    ('mon', 'days', 30),
                    ('year', 'days', 365)]
    try:
        tokens = relative.lower().split(' ')
        past = False
        if tokens[-1] == 'ago':
            past = True
            tokens =  tokens[:-1]
        elif tokens[0] == 'in':
            tokens = tokens[1:]


        units = dict(days = 0, seconds = 0, microseconds = 0)
        #we should always get pairs, if not we let this die and throw an exception
        while len(tokens) > 0:
            value = tokens.pop(0)
            if value == 'and':    #just skip this token
                continue
            else:
                value = float(value)

            unit = tokens.pop(0)
            for match, time_unit, time_constant in unit_mapping:
                if unit.startswith(match):
                    units[time_unit] += value * time_constant
        return datetime.timedelta(**units), past

    except Exception as e:
        raise ValueError("Don't know how to parse %s: %s" % (relative, e))

This can parse things like:

• 2 days ago
• in 60 seconds
• 2 DAY and 4 Secs
• in 1 year, 1 Month, 2 days and 4 MICRO
• 2 Weeks 4 secs ago
• 7 millis ago

A huge but: It simplifies month and year to 30 and 365 days respectively. Not always what you want, though it's enough for some cases.