I think they are not required, but recommended.

From https://www.python.org/dev/peps/pep-0008/#comments:

   You should use two spaces after a sentence-ending period in multi- sentence comments, except after the final sentence.

From https://www.python.org/dev/peps/pep-0012/#general:

   You must adhere to the Emacs convention of adding two spaces at the end of every sentence.

AFAIK in English typography the space after a sentence-ending period is longer than spaces between words. In other European typographies they have the same width.