input: Write a python function to generate a random letter from A to Z.
  assert generate_random_letter() in 'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
  assert isinstance(generate_random_letter(), str)
  assert len(generate_random_letter()) == 1
output: import random
  import string
  
  def generate_random_letter():
      return random.choice(string.ascii_uppercase)