Question about for loop not creating an infinite loop.

[ichabod801]

The pop method removes the last item from the list, as well as returning that item. So the first loop shrinks the list by one before growing it by one, thus keeping it the same size. The second one has no pop, so items are not removed (iterating with a for loop does not remove items from the list).

Note that modifying a list while you are iterating over it is a bad idea. It works out in the code above, but it doesn't always. A better way to do what your exercise wants is to build a new list:

great_magicians = []
for magician in magicians:
    the_great = 'the great {}'.format(magician)
    great_magicians.append(the_great)
    print(great_magicians)

The format method of strings is recommended over string addition for efficiency reasons. In 3.6 or later, look into f-strings.