Python function to round down minutes to a user specified resolution

gistfile1.txt

from datetime import datetime, timedelta

def round_minutes(dt, resolutionInMinutes):
    """round_minutes(datetime, resolutionInMinutes) => datetime rounded to lower interval
    Works for minute resolution up to a day (e.g. cannot round to nearest week).
    """

    # First zero out seconds and micros
    dtTrunc = dt.replace(second=0, microsecond=0)

    # Figure out how many minutes we are past the last interval
    excessMinutes = (dtTrunc.hour*60 + dtTrunc.minute) % resolutionInMinutes

    # Subtract off the excess minutes to get the last interval
    return dtTrunc + timedelta(minutes=-excessMinutes)