<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_namespace_keys(app, limit):
 """Get namespace keys."""

  ns_query = datastore.Query('__namespace__', keys_only=True, _app=app)
  return list(ns_query.Run(limit=limit, batch_size=limit))