Exploring __all__ in Practice

00:00 __all__ is more than a tool to facilitate wildcard imports from packages, or to limit unwanted objects from being exported. Instead, think of it as a way to define the public API of a module or package.

00:12 In practical terms, you can use it to deliver a simple, consistent set of exported names, to prevent the exposure of internal details like constants or imports, or to allow packages to re-export selected names from multiple modules.

00:25 All of these serve to make the module or package API explicit and predictable. Let’s explore this concept with an example of using __all__ in a module.

00:35 Back in the IDE, pokereader.py is a fun little module that pulls data from pokeapi.co. It has one class, two functions, and a constant.

00:45 Importantly, the _fetch_pokemon() function is a helper used by get_pokemon_data() as well as internally in the Pokemon class. It’s already marked with a leading underscore, so given what you know about wildcards, do you think you need to use __all__ here? Pop open the REPL to find out what happens when you import from this file.

01:04 Note that because this module uses requests, which is a third-party library, you will need to have it installed in your environment in order to run this code.

01:12 Okay, from pokereader import *,

01:15 run dir(),

01:17 and added to the global namespace you can see BASE_URL, Pokemon, get_pokemon_data(), and requests.

01:25 Maybe not what you expected? While _fetch_pokemon() was in fact skipped, you also ended up importing BASE_URL and the requests library. Remember, a wildcard import will find all of the public names, including requests and BASE_URL.

01:40 So to keep the API clean, you should define __all__ as a list holding the strings get_pokemon_data and Pokemon.

01:51 Save the file, restart the REPL, and try again.

01:58 from pokereader import *, call dir(), perfect. The only things added were Pokemon and get_pokemon_data(), which realistically are the only objects you would want a user to import.

02:11 Nice and clean.