input: Write a python function to count the number of vowels, consonants, and words in a string consisting only of alphabetic characters.
  assert calculate("hello") == (2, 3, 1)
  assert calculate("world") == (1, 4, 1)
  assert calculate("aeiou") == (5, 0, 1)
output: def calculate(s):
      vowels = "aeiouAEIOU"
      num_vowels = sum(1 for char in s if char in vowels)
      num_consonants = sum(1 for char in s if char.isalpha() and char not in vowels)
      num_words = len(s.split())
      return (num_vowels, num_consonants, num_words)