https://docs.python.org/3/tutorial/
https://docs.python.org/3/library/index.html#library-index
https://docs.python.org/3/reference/index.html#reference-index
https://docs.python.org/3/extending/index.html#extending-index
https://docs.python.org/3/tutorial/
https://docs.python.org/3/library/index.html#library-index
https://docs.python.org/3/reference/index.html#reference-index
https://docs.python.org/3/extending/index.html#extending-index