I have the following line of code: for i in [i for i,x in enumerate(catdate) if x == set(NNSRCfile['datetimenew']).intersection(catdate)]: print i I am trying to find the index of the intersection for the two components above. Both are lengthy lists that have several commonalities. The intersection part works perfectly; however, the for loop seems to output nothing. (ie: there is nothing that is printed). Python outputs no error, and when I run the code in IPython, I notice that i is equivalent to to the very last element in the list "catdate", instead of listing the indices of "catdate" that are equivalent to the intersection values. Any help is greatly appreciated!