input: Write a python function to get the value of a specified key from a dictionary and print it.
  assert get_value({"name": "John", "age": 40}, "name") == "John"
  assert get_value({"name": "John", "age": 40}, "age") == 40
  assert get_value({"name": "John", "age": 40}, "address") is None
output: def get_value(d, key):
      return d.get(key)