This function counts the number of vowels in a sentence.

def VowelCount(Sentence):  
  vowelList = "aeiouAEIOU"  
  total=0  
  for i in Sentence:  
    if i in vowelList:  
      total += 1  
  return total  


Sentence = "Jim wants to get a job in data science."  
print('''The number of vowels in "''' + Sentence + '''" is ''' + str(VowelCount(Sentence)))  

It gives an output like this:

The number of vowels in "Jim wants to get a job in data science." is 12