Which standard library modules are required to run the Python 3.5 interpreter?

Question

Here\'s a CPython program that tries to initialize the interpreter with an empty sys.path:

#include 

int main(int argc, char**          


        

Answer 1

These are packages/modules that are used during interpreter start-up (as, @Charles Duffy noted in a comment, by looking in sys.modules).

The result depends on whether you have site enabled or not (your Py_NoSiteFlag = 1; implies this isn't the case but anyway, I'll give both options :-)).

site drags a couple of additional modules with it when you use it like _sitebuiltins and stat, in total you could run Python using only the following:

abc.py               encodings       os.py         _sitebuiltins.py  sysconfig.py
codecs.py            genericpath.py  posixpath.py  site.py           _collections_abc.py  
io.py                stat.py         _weakrefset.py

with site disabled, you're stripped down to the following 6:

abc.py  codecs.py  encodings  io.py  os.py  _weakrefset.py

when invoked through C with Py_Initialize() (or through Windows based on your comment) I'm guessing os.py might not be actually needed.

Answer 2

Here's another approach - asking the Python interpreter what modules are loaded:

$ python3.5 -v -S -c '' |& grep SourceFileLoader | sort 
import 'abc' # <_frozen_importlib_external.SourceFileLoader object at 0x7f4b1d12e860>
import '_bootlocale' # <_frozen_importlib_external.SourceFileLoader object at 0x7f4b1d1367b8>
import 'codecs' # <_frozen_importlib_external.SourceFileLoader object at 0x7f4b1d187fd0>
import 'encodings.aliases' # <_frozen_importlib_external.SourceFileLoader object at 0x7f4b1d11eac8>
import 'encodings' # <_frozen_importlib_external.SourceFileLoader object at 0x7f4b1d187be0>
import 'encodings.latin_1' # <_frozen_importlib_external.SourceFileLoader object at 0x7f4b1d12e3c8>
import 'encodings.utf_8' # <_frozen_importlib_external.SourceFileLoader object at 0x7f4b1d12c898>
import 'io' # <_frozen_importlib_external.SourceFileLoader object at 0x7f4b1d12e5f8>
import '_weakrefset' # <_frozen_importlib_external.SourceFileLoader object at 0x7f4b1d135080>

_bootlocale is not required but recommended. It's used for initializing the best encoding for sys.stdin/sys.stdout/sys.stderr. See https://hg.python.org/cpython/rev/fbbf8b160e8d

sys.modules can lie as it's mutable.

Answer 3

If you run the interpreter as Charles Duffy suggests in his comment, you'll load packages like readline. It has been a decade since I did this but IIRC you don't need that module if you use python as an extension to your C program, as there is no commandline interaction. The same might hold for other modules.

The quickest way to determine what is really needed with only a slight chance of getting in too much is by putting all of lib/python3.5 where your program can find it, and in the program print out sys.modules, that will give you a list of what your program actually loaded, not what the interpreter might need to start up. After that remove everything not on that list.