Can't get program to print “not in sentence” when word not in sentence

Question

I have a program that asks for input of a sentence, then asks for a word, and tells you the position of that word:

sentence = input("enter sentence: ").lower()
askedword = input("enter word to locate position: ").lower()
words = sentence.split(" ")

for i, word in enumerate(words):
     if askedword == word :
          print(i+1)
    #elif keyword != words :
         #print ("this not")

However I cannot get the program to work correctly when I edit it to say that if the input word is not in the sentence, then print "this isn't in the sentence"

Answer 1

Lists are sequences, as such you can use the in operation on them to test for membership in the words list. If inside, find the position inside the sentence with words.index :

sentence = input("enter sentence: ").lower()
askedword = input("enter word to locate position: ").lower()
words = sentence.split(" ")

if askedword in words:
    print('Position of word: ', words.index(askedword))
else:
    print("Word is not in the given sentence.")

With sample input:

enter sentence: hello world

enter word to locate position: world
Position of word: 1

and, a false case:

enter sentence: hello world

enter word to locate position: worldz
Word is not in the given sentence.

If you're looking to check against multiple matches then a list-comprehension with enumerate is the way to go:

r = [i for i, j in enumerate(words, start=1) if j == askedword]

Then check on whether the list is empty or not and print accordingly:

if r:
    print("Positions of word:", *r)
else:
    print("Word is not in the given sentence.")

Answer 2

Jim's answer—combining a test for askedword in words with a call to words.index(askedword) —is the best and most Pythonic approach in my opinion.

Another variation on the same approach is to use try - except :

try:
    print(words.index(askedword) + 1) 
except ValueError:
    print("word not in sentence")

However, I just thought I'd point out that the structure of the OP code looks like you might have been attempting to adopt the following pattern, which also works:

for i, word in enumerate(words):
    if askedword == word :
        print(i+1)
        break
else:    # triggered if the loop runs out without breaking
    print ("word not in sentence")

In an unusual twist unavailable in most other programming languages, this else binds to the for loop, not to the if statement (that's right, get your editing hands off my indents). See the python.org documentation here.