<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def pad(obj, pad_length):
 """ Return a copy of the object with piano-roll padded with zeros at the end along the time axis. Parameters pad_length : int The length to pad along the time axis with zeros. """

    _check_supported(obj)
    copied = deepcopy(obj)
    copied.pad(pad_length)
    return copied