input: Write a function to provide a Python API for KB SRU. The function should create an instance of the "sru" class and allow users to call the "search" method with a query string and optional parameters for collection name, start record number, maximum number of records to return, and record schema. The method should return a "response" object containing the search results, from which specific information such as titles, creators, and subjects can be extracted using the various properties of the "response" object.
  
  
  def kb_sru_api(query, collection=None, startrecord=1, maximumrecords=1, recordschema=None):
      sru_instance = sru()
      response_object = sru_instance.search(query, collection=collection, startrecord=startrecord, maximumrecords=maximumrecords, recordschema=recordschema)
      return response_object
  
  assert isinstance(kb_sru_api("example query", "GGC"), response)
  assert isinstance(kb_sru_api("example query", "ANP", startrecord=1, maximumrecords=5), response)
  assert not kb_sru_api("nonexistent query")
  
output: def kb_sru_api(query, collection=None, startrecord=1, maximumrecords=1, recordschema=None):
      sru_instance = sru()
      response_object = sru_instance.search(query, collection=collection, startrecord=startrecord, maximumrecords=maximumrecords, recordschema=recordschema)
      return response_object