[First of all let me say I'm not all that familiar with Windows, so please let me know if the wording in my analysis below is not clear and/or misleading.]

It would appear the 32-bit installer for Python 2.7.11 creates the registry key:
---
HKLM\Software\Wow6432Node\Python\PythonCore\2.7\PythonPath
---
(...just like previous 2.7 versions did.)

However, registry accesses (PC/getpathp.c's getpythonpath()) are done like so:
---
    (...)
    keyBuf = keyBufPtr = PyMem_RawMalloc(keyBufLen);
    if (keyBuf==NULL) goto done;

    memcpy_s(keyBufPtr, keyBufLen, keyPrefix, sizeof(keyPrefix)-sizeof(WCHAR));
    keyBufPtr += Py_ARRAY_LENGTH(keyPrefix) - 1;
    mbstowcs(keyBufPtr, PyWin_DLLVersionString, versionLen);
    (...)
---
where 'PyWin_DLLVersionString' now is "2.7-32":
---
.rsrc:1E2760FA                 unicode 0, <2.7-32>,0
---
(it used to be "2.7" in previous versions) 


Thus, the key that python27.dll builds is:
 HKLM\Software\Wow6432Node\Python\PythonCore\2.7-32\PythonPath
and not
 HKLM\Software\Wow6432Node\Python\PythonCore\2.7\PythonPath

and consequently the runtime cannot build a proper sys.path, which causes embedded interpreters to fail loading core modules.

As a workaround, it seems renaming the registry key to its "-32"-suffixed name, does help.

Issue 24508 backported the project files from 3.5 to 2.7. In the new pyproject.props, MS_DLL_ID (for the DLL string table) is defined as the value of SysWinVer. Currently the latter is defined in python.props as follows:

    <!-- The version number for sys.winver -->
    <SysWinVer>$(MajorVersionNumber).$(MinorVersionNumber)</SysWinVer>
    <SysWinVer Condition="$(Platform) == 'Win32' or $(Platform) == 'x86'">$(SysWinVer)-32</SysWinVer>

AFAIK, 2.7 shouldn't be using the -32 suffix for 32-bit builds. This should only have changed for 3.5+.

Eryk is correct, there should be no -32 suffix in 2.7.  It's simple enough to fix, just remove the last line Eryk quoted (and purge generated files from PC/).

This is a pretty major bug; Benjamin and Steve, how do you want to deal with it?

Needs a new release - up to Ben whether it's .12 or just a new .11. I can do the build today or this weekend, but not in between.

I don't really have the time to cut a new release in the next few weeks.

On Tue, Dec 8, 2015, at 10:42, Steve Dower wrote:
> 
> Steve Dower added the comment:
> 
> Needs a new release - up to Ben whether it's .12 or just a new .11. I can
> do the build today or this weekend, but not in between.
> 
> ----------
> 
> _______________________________________
> Python tracker <report@bugs.python.org>
> <http://bugs.python.org/issue25824>
> _______________________________________

This issue specifically talks about the 32-bit installer but the 64-bit is also affected by it.

It is the same workaround but with a different registry key:

  HKLM\Software\Python\PythonCore\2.7

renamed to

  HKLM\Software\Python\PythonCore\2.7-32

64-bit Python shouldn't have the -32 in sys.winver, so it isn't affected. (If it does have the suffix, we have a second issue, but since it'd also be fixed by removing the code Eryk quoted there's no need for another issue.)

In a interactive shell:

$ python
Python 2.7.11 (v2.7.11:6d1b6a68f775, Dec  5 2015, 20:40:30) [MSC v.1500 64 bit (AMD64)] on win32
Type "help", "copyright", "credits" or "license" for more information.
>>> import sys
>>> sys.winver
'2.7-32'
>>>

I agree that this is the same fix but I think the title should be updated.

Note this issue breaks Vim compiled with python support (issue: https://github.com/vim/vim/issues/526) and ci.appveyor.com tests (e.g. https://ci.appveyor.com/project/chrisbra/vim/build/211)

Our installations of Python Essentials for SPSS Statistics 21 (64bit, presumeably also 32bit) were also broken by this issue (Python Essentials for SPSS 21 uses the regular Python 2.7 folder/installation).

The workaround with renaming the mentioned registry key works here as well (we still decided to hold back the update to Python 2.7.11 for the moment).

New changeset b91c323a605e by Steve Dower in branch '2.7':
Issue #25824: Fixes sys.winver to not include any architecture suffix.
https://hg.python.org/cpython/rev/b91c323a605e