input: Write a function to generate SHA-1 hash of a given string.
  assert get_hash("hello") == "f7c3bc1d808e04732adf679965ccc34ca7ae3441"
  assert get_hash("world") == "7c211433f02071597741e6ff5a8ea34789abbf43"
  assert get_hash("test") == "a94a8fe5ccb19ba61c4c0873d391e987982fbbd3"
output: def get_hash(input_string):
      import hashlib
      return hashlib.sha1(input_string.encode()).hexdigest()