Can anyone solved isogram detector ?

Question

In Coad Coach section

Answer 1

That was a long time ago, I can no longer remember.

Answer 2

Show your attempt to can help you with mistakes

Answer 3

word=input()
list_word=list(word)
n=0
while n < len(list_word):
if list_word.count(list_word[n]) == 1:
n+=1
else:
break
if n==len(list_word):
print ("true")
else:
print ("false")