varSentence = ("The fat cat sat on the mat")print (varSentence)varWord = input("Enter word ")varSplit = varSentence.split()if varWord in varSplit:print ("Found word")
else:print ("Word not found")for (num, x) in enumerate(sentence):if word == x:print ("Your word is in position",num,"!")

No need for a loop, use list.index, protected by a try/except block in case string is not found. list.index returns the first occurence of the word.

sent = 'ASK NOT WHAT YOUR COUNTRY CAN DO FOR YOU ASK WHAT YOU CAN DO FOR YOUR COUNTRY.'
words = sent.split()
word = "WHAT"try:print(words.index(word)+1)
except ValueError:print("{} is not in the sentence".format(word))

returns 3 because index found the word at the 3rd position (and arrays start at 0)