cc @pablogsal @nascheme

It seems more useful to me to add a little function to _imp. E.g. _imp.list_frozen_modules(). That's close to the same amount of code as your _testembed change and could be potentially useful in other ways. If you prefer, could be hidden function like _imp._list_frozen_modules(). Returns a list of frozen module names.

It seems more useful to me to add a little function to _imp. E.g. _imp.list_frozen_modules().

What would be the use case for listing stdlib frozen modules? I didn't add any function because I failed to find an use case.

It seems like sys.builtin_module_names is used in many places since built-in modules are special.

_frozen_importlib and _frozen_importlib_external are really special, since they are the frozen version of Python modules, but under a different name.

The only module which might matter is zipimport. CPython 3.10 exposes it as a frozen module. You can check it using its loader class (FrozenImporter):

$ ./python
Python 3.10.0a6+
>>> import zipimport
>>> zipimport.__loader__
<class '_frozen_importlib.FrozenImporter'>

I guess that the only people who really care are people creating their own Python binary with their own list of frozen modules. But I guess that they know what they put in the binary.

I merged this PR to be able to work on https://bugs.python.org/issue43456

@nascheme: If you consider that it's useful to have an API to list frozen modules, feel free to propose a new PR for that.