helpers.py

def get_changeset_path_for(utctime):
    import os
    parts = ["http://planet.osm.org/replication/changesets/"]
    from math import floor
    minutes = int(floor((utctime - config.OSM_DAY_ZERO).total_seconds() / 60))
    rem = minutes
    while rem > 0:
        parts.append(str(rem % 1000).zfill(3))
        rem = (rem - rem % 1000) / 1000
    return os.path.join(*parts)

Where

OSM_DAY_ZERO = datetime.datetime(2012, 10, 28, 19, 36, tzinfo=tzutc())