docs: def normalize_date(date):
          '''normalize the specified date to milliseconds since the epoch
  
          If it is a string, it is assumed to be some sort of datetime such as
          "2015-12-27" or "2015-12-27T11:01:20.954". If date is a naive datetime,
          it is assumed to be UTC.
  
          If numeric arguments are beyond 5138-11-16 (100,000,000,000 seconds
          after epoch), they are interpreted as milliseconds since the epoch.
          '''
  
          if isinstance(date, datetime):
              pass
          elif date == "now":
              date = datetime.now(pytz.UTC)
          elif isinstance(date, (basestring, int, float, long)):
              try:
                  ts = float(date)
                  if ts > MAX_TS_SECONDS:
                      # ts was provided in ms
                      ts = ts / 1000.0
                  # For unix timestamps on command line
                  date = datetime.utcfromtimestamp(float(ts))
              except ValueError:
                  try:
                      date = dateparse(date)
                  except ValueError as e:
                      raise InvalidDatalakeMetadata(str(e))
          else:
              msg = 'could not parse a date from {!r}'.format(date)
              raise InvalidDatalakeMetadata(msg)
  
          return Metadata._from_datetime(date)