Issue 24769: Interpreter doesn't start when dynamic loading is disabled

When attempting to build Python without dynamic loading (HAVE_DYNAMIC_LOADING is not defined), the module "_imp" will not have the function "exec_dynamic."  However, Lib/bootstrap.py seems to assume that "_imp.exec_dynamic" exists, causing the error:

----
./python -E -S -m sysconfig --generate-posix-vars ;\
if test $? -ne 0 ; then \
	echo "generate-posix-vars failed" ; \
	rm -f ./pybuilddir.txt ; \
	exit 1 ; \
fi
Traceback (most recent call last):
  File "<frozen importlib._bootstrap>", line 1134, in _install
  File "<frozen importlib._bootstrap>", line 1114, in _setup
  File "<frozen importlib._bootstrap>", line 1082, in _builtin_from_name
  File "<frozen importlib._bootstrap>", line 673, in _load_unlocked
  File "<frozen importlib._bootstrap>", line 748, in exec_module
AttributeError: module '_imp' has no attribute 'exec_dynamic'
Fatal Python error: Py_Initialize: importlib install failed

Current thread 0x00000000 (most recent call first):
ABNORMAL TERMINATION
generate-posix-vars failed
----

when trying to build.  This error means that Python 3.5 will not be able to build in a purely static (no dynamic loading whatsoever) form.

This error was encountered in Python 3.5b4.

This is an interesting find - thanks.

Adding Larry as 3.5 release manager to the cc here, as I think the right fix actually involves an API adjustment inside _imp.

One of the consequences of PEP 489 (multi-phase initialisation) was that builtin imports and extension module imports now share a lot more code, and that includes the fact that while we have both _imp.create_builtin and _imp.create_dynamic, they currently share a module level exec implementation in _imp.exec_dynamic.

However, the definition and implementation of _imp.exec_dynamic is still behind the same preprocessor guard as _imp.create_dynamic, hence the error reported here.

As far as a fix goes, rather than defining _imp.exec_dynamic unconditionally, my inclination is to say that merging the Python level APIs in addition to the underyling C level implementation represents a design mistake when we implemented the PEP, and there should be a separate _imp.exec_builtin function.

The fact that _imp.exec_dynamic just called _imp.exec_builtin internally would then be a pure CPython implementation detail, rather than something importlib specifically depended on.

Apologies for the delay; I was on vacation.

This was indeed a mistake in PEP 489 implementation. I agree with Nick on the solution.
Here is a patch that adds exec_builtin, with implementation shared with exec_dynamic.

Looks fine to me.  Nick had suggested calling exec_builtin from exec_dynamic (to the same effect as your patch), but I don't consider that much of an issue. :)

Right. I think a common helper is cleaner than calling a clinic-generated wrapper.

Uh, Nick?  You didn't add me to this bug.

Patch looks good to me too. I think this needs to be put forward as a PR to bitbucket right? It looks Release Critical to me.

It's ultimately Larry's call, but I think it should go into 3.5.0.

Yes, I'll accept this into 3.5.0, please send a pull request.

I wanted to get this in to Python 3.5.0rc2, so I checked it in myself.  Petr, I gave you credit in the checkin comment and Misc/NEWS.  Hope that's okay!

Thanks Larry! Sorry I didn't get to this as soon as I got back from the US.

Will you add it to 3.5.1 and 3.6.0, or would you prefer I take care of that?

I pulled the 3.5 branch a few minutes ago, and the patch isn't present.  Has it not been pushed to hg.python.org?

That's correct, it's just in 3.5.0 at the moment.

I have merged it forward into 3.5.1 and 3.6.

New changeset 931593401e3e by Larry Hastings in branch '3.5':
Issue #24769: Interpreter now starts properly when dynamic loading
https://hg.python.org/cpython/rev/931593401e3e

resolution: fixed
stage: commit review -> resolved