input: Write a python function to parse a JSON string and convert it to a Python dictionary.
  assert parse_json_string('{"name": "John", "age": 30, "city": "New York"}') == {"name": "John", "age": 30, "city": "New York"}
  assert parse_json_string('{"fruit": "Apple", "size": "Large", "color": "Red"}') == {"fruit": "Apple", "size": "Large", "color": "Red"}
  assert parse_json_string('{"success": true, "error": null}') == {"success": True, "error": None}
output: import json
  
  def parse_json_string(json_string):
      return json.loads(json_string)