Do not add an autoload comment unless it is really necessary. Autoloading code means it is always globally visible. Once an item is autoloaded, there is no compatible way to transition back to it not being autoloaded (after people become accustomed to being able to use it without an explicit load).
python-modefunction, so that people can simply use M-x python-mode to load the library.
(defvar foo)to silence an undefined variable warning, and
declare-function(see Declaring Functions) to silence an undefined function warning; or require the relevant library; or use an explicit autoload statement.