bpo-40854: Allow overriding sys.platlibdir via PYTHONPLATLIBDIR env-var#20605

manisandro

You can currently point the python interpreter to a different install say via

export PYTHONHOME=<Prefix>
export PYTHONPATH=<Prefix>/lib/python3.9
python3

With the newly added platlibdir [1], if python was configured with platlibdir=lib64, this will break because i.e. the site-packages dir as returned by sysconfig.get_paths() will use lib64 and not lib as the other install may be using.

This PR adds the possibility to override the platlibdir via environment variable.

Full rationale: [2].

[1] #8068
[2] https://src.fedoraproject.org/rpms/python3.9/pull-request/10

https://bugs.python.org/issue40854

the-knights-who-say-ni

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vstinner

See https://pythondev.readthedocs.io/pyconfig.html#add-an-environment-variable for the different steps to add a new environment variables:

Update usage_xxx to document the new env var
Doc/using/cmdline.rst: Document the new env var
Misc/python.man: Document the new env var
You may also mention it at https://docs.python.org/dev/library/sys.html#sys.platlibdir

bedevere-bot

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

manisandro

@vstinner Thanks for your prompt feedback, I've reworked the PR

hroncok

@manisandro Could you please copy paste and use the phrase as suggested by the bot? It will label this PR accordingly.

manisandro

I have made the requested changes; please review again

bedevere-bot

Thanks for making the requested changes!

@vstinner: please review the changes made to this pull request.

vstinner

Thanks, the update PR is much better! New review.

Please document also the new PyConfig field in https://docs.python.org/dev/c-api/init_config.html#c.PyConfig documentation with a ".. versionadded:: 3.10" markup.

bedevere-bot

A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

manisandro

I have made the requested changes; please review again

bedevere-bot

Thanks for making the requested changes!

@vstinner: please review the changes made to this pull request.

vstinner

It seems possible to test a custom PYTHONPATHLIBDIR in test_embed. At least, the following patch worked for me:

diff --git a/Lib/test/test_embed.py b/Lib/test/test_embed.py
index 3b551e9015..f1371db866 100644
--- a/Lib/test/test_embed.py
+++ b/Lib/test/test_embed.py
@@ -586,13 +586,14 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             if value is self.GET_DEFAULT_CONFIG:
                 expected[key] = config[key]
 
-        pythonpath_env = expected['pythonpath_env']
-        if pythonpath_env is not None:
-            paths = pythonpath_env.split(os.path.pathsep)
-            expected['module_search_paths'] = [*paths, *expected['module_search_paths']]
-        if modify_path_cb is not None:
-            expected['module_search_paths'] = expected['module_search_paths'].copy()
-            modify_path_cb(expected['module_search_paths'])
+        if expected['module_search_paths'] is not self.IGNORE_CONFIG:
+            pythonpath_env = expected['pythonpath_env']
+            if pythonpath_env is not None:
+                paths = pythonpath_env.split(os.path.pathsep)
+                expected['module_search_paths'] = [*paths, *expected['module_search_paths']]
+            if modify_path_cb is not None:
+                expected['module_search_paths'] = expected['module_search_paths'].copy()
+                modify_path_cb(expected['module_search_paths'])
 
         for key in self.COPY_PRE_CONFIG:
             if key not in expected_preconfig:
@@ -765,6 +766,8 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'buffered_stdio': 0,
             'user_site_directory': 0,
             'faulthandler': 1,
+            'platlibdir': 'my_platlibdir',
+            'module_search_paths': self.IGNORE_CONFIG,
 
             'check_hash_pycs_mode': 'always',
             'pathconfig_warnings': 0,
@@ -796,6 +799,8 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'user_site_directory': 0,
             'faulthandler': 1,
             'warnoptions': ['EnvVar'],
+            'platlibdir': 'env_platlibdir',
+            'module_search_paths': self.IGNORE_CONFIG,
             '_use_peg_parser': 0,
         }
         self.check_all_configs("test_init_compat_env", config, preconfig,
@@ -824,6 +829,8 @@ class InitConfigTests(EmbeddingTestsMixin, unittest.TestCase):
             'user_site_directory': 0,
             'faulthandler': 1,
             'warnoptions': ['EnvVar'],
+            'platlibdir': 'env_platlibdir',
+            'module_search_paths': self.IGNORE_CONFIG,
             '_use_peg_parser': 0,
         }
         self.check_all_configs("test_init_python_env", config, preconfig,
diff --git a/Makefile.pre.in b/Makefile.pre.in
index 1d0bd32ffb..a7d5dd2945 100644
--- a/Makefile.pre.in
+++ b/Makefile.pre.in
@@ -782,9 +782,7 @@ Programs/python.o: $(srcdir)/Programs/python.c
 	$(MAINCC) -c $(PY_CORE_CFLAGS) -o $@ $(srcdir)/Programs/python.c
 
 Programs/_testembed.o: $(srcdir)/Programs/_testembed.c
-	$(MAINCC) -c $(PY_CORE_CFLAGS) \
-		-DPLATLIBDIR='"$(PLATLIBDIR)"' \
-		-o $@ $(srcdir)/Programs/_testembed.c
+	$(MAINCC) -c $(PY_CORE_CFLAGS) -o $@ $(srcdir)/Programs/_testembed.c
 
 Modules/_sre.o: $(srcdir)/Modules/_sre.c $(srcdir)/Modules/sre.h $(srcdir)/Modules/sre_constants.h $(srcdir)/Modules/sre_lib.h
 
diff --git a/Programs/_testembed.c b/Programs/_testembed.c
index c6a0d6c9e0..7621c46260 100644
--- a/Programs/_testembed.c
+++ b/Programs/_testembed.c
@@ -549,7 +549,7 @@ static int test_init_from_config(void)
     /* FIXME: test path config: module_search_path .. dll_path */
 
     putenv("PYTHONPLATLIBDIR=env_platlibdir");
-    status = PyConfig_SetBytesString(&config, &config.platlibdir, PLATLIBDIR);
+    status = PyConfig_SetBytesString(&config, &config.platlibdir, "my_platlibdir");
     if (PyStatus_Exception(status)) {
         PyConfig_Clear(&config);
         Py_ExitStatusException(status);
@@ -676,7 +676,7 @@ static void set_most_env_vars(void)
     putenv("PYTHONFAULTHANDLER=1");
     putenv("PYTHONIOENCODING=iso8859-1:replace");
     putenv("PYTHONOLDPARSER=1");
-    putenv("PYTHONPLATLIBDIR="PLATLIBDIR);
+    putenv("PYTHONPLATLIBDIR=env_platlibdir");
 }

manisandro

Thanks, added to PR.

vstinner

Ok, the PR now looks complete: all documentations are updated, thanks!

I didn't expect the new sys.platlibdir to land into PyConfig, but I think that I understood the rationale in https://bugs.python.org/issue40854

Overriding PYTHONHOME is uncommon. If you do that, I'm not surprised that you fall into corner cases. So having the ability to override platlibdir sounds reasonable.

Hum. It seems like PyConfig.platlibdir is a parameter which affects the "Path Configuration". So please add it to "Path configuration inputs" at:
https://docs.python.org/dev/c-api/init_config.html#path-configuration

…able

manisandro

Thanks, I've updated the PR accordingly.

vstinner

Oh, one last request, sorry!

When you update a PR, please add a new commit rather than always rebase/squash your commits. New commits help to see what has been modified since my latest review.

manisandro

No problem, pushed as new commit.

vstinner

Thanks, I merged your PR.

manisandro

Thank you for merging and for the review!

…ar (GH-20605) (GH-20725) (cherry picked from commit 8f023a2) Co-authored-by: Sandro Mani <manisandro@gmail.com>

the-knights-who-say-ni added the CLA not signed label Jun 3, 2020

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manisandro changed the title ~~bpo-40854: Allow overriding sys.platlibdir via _PYTHON_PLATLIBDIR env-var~~ Jun 3, 2020

the-knights-who-say-ni added CLA signed and removed CLA not signed labels Jun 3, 2020

manisandro requested a review from vstinner June 4, 2020 00:18

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bedevere-bot requested a review from vstinner June 5, 2020 10:18

vstinner reviewed Jun 7, 2020

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Allow overriding sys.platlibdir via PYTHONPLATLIBDIR environment vari… …

a22a8e3

…able

vstinner reviewed Jun 8, 2020

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Add check to ensure PLATLIBDIR is defined

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vstinner merged commit 8f023a2 into python:master Jun 8, 2020

bedevere-bot removed the awaiting change review label Jun 8, 2020

vstinner added a commit that referenced this pull request Jun 8, 2020

bpo-40854: Allow overriding sys.platlibdir via PYTHONPLATLIBDIR env-v… …

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…ar (GH-20605) (GH-20725) (cherry picked from commit 8f023a2) Co-authored-by: Sandro Mani <manisandro@gmail.com>

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