sphinx_theme_builder._internal.cli calls sys.exit() on module import, breaking pydoc, module introspection

[ferdnyc]

If a project dependency is missing, the __init__.py for sphinx_theme_builder._internal.cli will call sys.exit(1) on import, making it impossible to examine the module via normal Python introspection tools like importlib.import_module() or pydoc.

Worse, a user who attempts to run a documentation keyword search from the command line using pydoc -k <keyword> will find their scan abruptly terminates as soon as pydoc reaches the module.

Even just typing import sphinx_theme_builder._internal.cli in a REPL will instantly drop the user out of their Python session, destroying any and all work they'd done with it up to that point:

$ python3
Python 3.11.2 (main, Feb  8 2023, 00:00:00) [GCC 12.2.1 20221121 (Red Hat 12.2.1-4)] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import sphinx_theme_builder._internal.cli
error: missing-command-line-dependencies

× Could not import a package that is required for the `stb` command line.
╰─> No module named 'sphinx_autobuild'

note: The optional cli dependencies of this package are missing.
hint: During installation, make sure to include the `[cli]`. For example:
      pip install "sphinx-theme-builder[cli]"
link: 
https://sphinx-theme-builder.rtfd.io/errors/#missing-command-line-dependencies

$

sys.exit() should only ever be called either inside a function (which isn't executed on import), or when inside an if __name__ == '__main__': conditional block. It's never OK to take down the entire interpreter with an exit() call at the module level, where it can be executed on import. (Especially for "optional" dependencies!) Following that rule is just part of being a polite and respectful member of the package ecosystem.

[pradyunsg]

Why are you importing an _internal submodule directly?

[ferdnyc]

As I said, one reason is when doing a command-line pydoc -k search.

[pradyunsg]

Adding a cross-reference for posterity: https://discuss.python.org/t/guidance-on-importability-of-installed-modules/25422

[pradyunsg]

Specifying a -k flag before the argument will search the synopsis lines of all available modules for the keyword given as the argument, again in a manner similar to the Unix man command. The synopsis line of a module is the first line of its documentation string.

Fair enough -- I've elaborated on my concerns over on the discuss.python.org thread. :)