input: Write a python function to count the number of vowels in a given sentence.
  assert countVowels("This is a sample sentence") == 7
  assert countVowels("Hello World") == 3
  assert countVowels("Python") == 1
output: def countVowels(sentence):
      vowels = "aeiouAEIOU"
      return sum(1 for char in sentence if char in vowels)