input: Write a function to implement the Python API for KB SRU. The function should create an instance of the "sru" class and perform a search using the "search" method, passing in a query string and optionally a collection name, start record number, maximum number of records to return, and record schema. The search method will return a "response" object containing the results of the search. The function should return the titles of the search results.
  
  def search_kbsru(query, collection=False, startrecord=1, maximumrecords=1, recordschema=False):
      sru_instance = sru()
      response_obj = sru_instance.search(query, collection, startrecord, maximumrecords, recordschema)
      if response_obj:
          return response_obj.titles
      return []
  
  assert search_kbsru("python", "GGC") == ["Python Programming", "Python for Data Science"]
  assert search_kbsru("data", "DPO", 1, 3) == ["Data Science", "Data Analysis", "Data Visualization"]
  assert search_kbsru("machine learning") == []
  assert search_kbsru("") == []
output: def search_kbsru(query, collection=False, startrecord=1, maximumrecords=1, recordschema=False):
      sru_instance = sru()
      response_obj = sru_instance.search(query, collection, startrecord, maximumrecords, recordschema)
      if response_obj:
          return response_obj.titles
      return []