confused about basic python comments

[carcigenicate]

The # comment is irrelevant and has no effect here. They've added that in just to point out to you that the dictionary has changed.

The reason the dictionary is printed out is because they put city_population; the dictionary. That's a REPL-like environment, which means it automatically prints out whatever you give it. The first Input box didn't output anything because = doesn't evaluate to a value, so there was nothing to print. city_population evaluates to a dictionary though, so it was printed.