Proposed modification in site.py allows "sitevendor" customization plugin in addition to existed "sitecustomize" and "usercustomuze". More info displayed when "python.exe -m site" typed from command line.
Vendors of Python sites (like Anaconda) can place there their own startup code. Mentioned "sitecustomize"  and "usercustomuze" works as before.

This is a larger issue then the PR might lead one to believe. Have you had discussion on python-ideas or in other forums about this?

Why is sitevendor required in addition to sitecustomize?

"sitevendor" is required because "sitecustomize" already "taken": imagine
organization XYZ , they install Python/Anaconda for workers in XYZ. Admin
in XYZ places some XYZ-specific code into "sitecustomize". As to "usersite"
- each worker of XYS uses it for their own purposes. This is what we have
now now (in general, as far as I understand the story).

Now we have Anaconda in addition to Python distribution. Where do we
suppose to place startup related code, which is different between Python
and Anaconda ? Example: sys.path to load python py-modules and
os.environ['PATH'] to load DLLs. Anaconda already uses some crazy patch in
Python/main.c code and it is controlled by environment variables like
CONDA_DLL_SEARCH_MODIFICATION_ENABLE. Somebody like you have to explain
Anaconda developers that following sitevendor.py shipped with Anaconda may
solve this problem (as alternative to patching C code). Real problem in
Anaconda is following: attempt to run "python.exe -m conda update --all"
gives error in SSL access to update server. Problem is that OpenSSL.dll was
moved into PythonHome\Lib\Bin and can't be loaded from there when I run
python.exe without activate.bat. Anaconda already solve this problem using
above CONDA_DLL_SEARCH_MODIFICATION_ENABLE and it is totally crazy and it
introduce problem how to set this variable. They can solve it by shipping
sitevendor.py as of:

import os
import sys
prefix = os.path.split(os.path.abspath(sys.executable))[0]
env = os.environ
env['CONDA_DLL_SEARCH_MODIFICATION_ENABLE'] = '1'
env['CONDA_DEFAULT_ENV'] = 'base'
env['CONDA_PREFIX'] = prefix
env['CONDA_SHLVL'] = '1'
# end of first sitevendor example

Next sitevendor.py example presented below:

# this sitevendor.py can theoretically be shipped with Anaconde if they
want, it works for me even without
# any CONDA_DLL_SEARCH_MODIFICATION_ENABLE
import os
import sys
import site
from os.path import join, pathsep

prefix = os.path.split(os.path.abspath(sys.executable))[0]

new_paths = pathsep.join([
  prefix, # not required if we start python[w].exe from prefix folder
  join(prefix, "Library", "mingw-w64", "bin"),
  join(prefix, "Library", "usr", "bin"),   # if not exist: see
removeduppath_ex(, True)
  join(prefix, "Library", "bin"),
##join(prefix, "Scripts")
])

L = []  # empty array for folders from path
env = os.environ
strpath = new_paths + pathsep + env['PATH'];

# string with combined path to array of folders:
for dir in strpath.split(';') :
   L.append(dir);
   ####print("dir=%s" % (dir))

# remove duplicated and nonexested folders
site.removeduppaths_ex(L , True)
strpath = pathsep.join(L);

### modify environment variables for current process
env['PATH'] = strpath;
env['CONDA_PREFIX'] = prefix
###env['CONDA_DLL_SEARCH_MODIFICATION_ENABLE'] = '1'

# Python module search path:
site.removeduppaths_ex(sys.path , True) # True to remove nonexistent
folder/files

# eof

On Mon, May 13, 2019 at 6:01 AM STINNER Victor <report@bugs.python.org>
wrote:

>
> Change by STINNER Victor <vstinner@redhat.com>:
>
>
> ----------
> nosy: +vstinner
>
> _______________________________________
> Python tracker <report@bugs.python.org>
> <https://bugs.python.org/issue36891>
> _______________________________________
>

> vx1920 <vx1920@gmail.com> added the comment:
>
> "sitevendor" is required because "sitecustomize" already "taken": imagine
> organization XYZ , they install Python/Anaconda for workers in XYZ. Admin
> in XYZ places some XYZ-specific code into "sitecustomize".

I don't think it's common situation.
If distribution want to add such "admin"-customization, distributors can
implement such additional customization in sitecustomize.py, or even in site.py.

For example, Ubuntu uses customized site.py and sitecustomize.py.

Is there some discussion in Anaconda developers about proposing "sitevendor"
is upstream (CPython)?  Or is it just your idea?

I dislike the proposed feature. site already allows sitecustomize and usercustomize.

If you distribute Python, you can modify site.py anyway. I suggest to close (reject) this feature.

I closed this because this proposal is not discussed well in conda community.
See https://github.com/python/cpython/pull/13246#issuecomment-492447317