input: Write a python function to parse a JSON string and extract the value associated with the key 'name'.
  assert extract_name('{"name": "John", "age": 30}') == 'John'
  assert extract_name('{"name": "Alice", "age": 25}') == 'Alice'
  assert extract_name('{"name": "Bob", "age": 40}') == 'Bob'
output: import json
  
  def extract_name(json_string):
      data = json.loads(json_string)
      return data['name']