Question

Is there any advantage to using keys() function?

for word in dictionary.keys():
    print word

vs

for word in dictionary:
    print word

Answer 1

Yes, in Python 2.x iterating directly over the dictionary saves some memory, as the keys list isn’t duplicated.

You could also use .iterkeys(), or in Python 2.7, use .viewkeys().

In Python 3.x, .keys() is a view, and there is no difference.

So, in conclusion: use d.keys() (or list(d.keys()) in python 3) only if you need a copy of the keys, such as when you’ll change the dict in the loop. Otherwise iterate over the dict directly.