<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def get_id_constraints(pkname, pkey):
 """Returns primary key consraints. :pkname: if a string, returns a dict with pkname=pkey. pkname and pkey must be enumerables of matching length. """

  if isinstance(pkname, str):
    return {pkname: pkey}
  else:
    return dict(zip(pkname, pkey))