Python time quantizer

quantize_time.py

"""
A simple time quantizer for python. Takes in a time and gives back the
quantized time given resolution in seconds. Always rounds down.
"""

from datetime import datetime


def quantize_time(time, resolution):
    """Round a time object to the previous time appropriate for resolution"""

    if not time or not isinstance(time, datetime):
        raise ValueError(
            'time parameter is required and must be a datetime instance')

    if not resolution or not isinstance(resolution, int) or resolution < 1:
        raise ValueError('resolution parameter must be a supported resolution')

    factors_60 = (1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30)

    # <1 minute
    if resolution in factors_60:
        quantized_second = int(floor(time.second/resolution)*resolution)
        return time.replace(microsecond=0, second=quantized_second)

    # <1 hour
    if resolution in [60*x for x in factors_60]:
        resolution = resolution/60
        quantized_minute = int(floor(time.minute/resolution)*resolution)
        return time.replace(microsecond=0, second=0, minute=quantized_minute)

    # <1 day
    if resolution in [60*60*x for x in (1, 2, 3, 4, 6, 8, 12)]:
        resolution = resolution/(60*60)
        quantized_hour = int(floor(time.hour/resolution)*resolution)
        return time.replace(microsecond=0, second=0, minute=0,
                            hour=quantized_hour)

    # 1 day
    if resolution == 60*60*24:
        return time.replace(microsecond=0, second=0, minute=0, hour=0)

    # 1 week
    if resolution == 60*60*24*7:
        quantized_day = time.day - time.weekday() # Week starts on Monday

        # If the quantized day is in the current month
        if quantized_day > 0:
            return time.replace(microsecond=0, second=0, minute=0, hour=0,
                                day=quantized_day)

        # Otherwise, it must be in the previous month, and we should decrement
        # month in the date
        else:
            month = time.month - 1
            year = time.year

            # If the quantized month is in the prevous year
            if month < 1:
                month = 12
                year = time.year - 1

            quantized_day = calendar.monthrange(year, month)[1] + quantized_day
            
            return time.replace(microsecond=0, second=0, minute=0, hour=0,
                                day=quantized_day, month=month, year=year)


    raise ValueError('Resolution not supported')