Don't require .py extension

[FRidh]

pytype refuses to operate on Python code that has no extension (as is typically done with executables).

[rchen152]

This probably has something to do with importlab's (https://github.com/google/importlab) assumption in a few places that Python files have a ".py" extension - I'll take a look!

[gpshead]

Related: we're introducing a .py3 file extension internally in a few places where code for both 2 and 3 is different and needs to coexist. Though that'll be more common within an occasional library than it will be for a main entry point file. (a .py3 when present takes priority over a potential .py file, only if being analyzed from a Python 3 perspective)

[martindemello]

how does python's own import resolution mechanism handle files that don't end with .py?

[gpshead]

It doesn't. We've patched our python3 interpreter internally do accept py3 as a suffix (a relatively small change). But the main file isn't actually imported so it doesn't have any name restrictions imposed by the interpreter.

[rchen152]

Unfortunately, I haven't had time to look at this yet - unassigning myself because we have a fixit starting next week, and someone else may want to work on this.

[ritwik12]

I can see that this issue is caused by https://github.com/google/importlab/blob/29a6ec92d3be80fce0edf019d769852e9fc71714/importlab/utils.py#L69

I would like to take this one. Please let me know.

[martindemello]

that would be great! i'd be happy to do the code review.

now that importlab handles unreadable files it might be enough just to remove the check for .py from expand_source_files and add a couple of tests to verify the behaviour for python and non-python files without an extension.

[rchen152]

Thanks for taking this on! I think https://github.com/google/pytype/blob/master/pytype/tools/analyze_project/pytype_runner.py#L199 would also need to be changed to not filter out non-.py files.

[ritwik12]

@rchen152 Done, Thanks for helping.