How to get the index in the 'in' statement in Python

I wrote an if statement like:

if word in vocab:
    print word

However, I also would like to know the matched word index in vocab.

Is there any way in Python can do this?

I just come up a solution that use vocab.index(word) to get the index, but this way go through the array twice (one in if statement, one call index()). I wonder there should be more efficiency method.

Thanks.

Answer

To avoid one loop, you can use a try-except clause (without using if ... in ...:)

try:
    i = vocab.index(word)
except ValueError as e:
    print e # Optional

    i = -1