What are the conditions where pyc files in a virtualenv will be created as symlinks?

Question

We have a virtualenv in our deploy environment where the .pyc files are sym links - particularly those in <venv_root>/lib/python2.7/ . Under what conditions does this happen?

Our environment:

• CentOS 7
• Python 2.7.5
• virtualenv 16.0.0
• some (but not all) python processes running on other servers with the virtualenv available via NFS (with write permissions)
• virtualenv created on a different filesystem to the root filesystem

I'm used to seeing the .py files in <venv_root>/lib/python2.7/ sometimes being symlinks. I know I can use the --always-copy flag to stop the .py files being symlinks. But I'm used to the .pyc files always being plain files.

Experiments I've tried (on the server in question):

• create fresh virtualenv on root filesystem
  • pyc files created as files
• run scripts using the virtualenv on the NFS host and the NFS client
  • no change to pyc files
• touch lib/python2.7/os.py and re-run scripts
  • no change to pyc files
• remove lib/python2.7/os.pyc and re-run scripts
  • runs on the NFS host, the pyc file is created as a normal file
  • runs on the NFS client, the pyc file is created as a normal file

To repeat the key question - under what conditions will I end up with .pyc files being sym links?

Here is a full listing of the virtualenv directory in question:

[root@appname-master]# ls -l /export/appname/common/venv/5_4_1/lib/python2.7/
total 68
lrwxrwxrwx   1 appname appname    31 Nov  8 04:17 _abcoll.py -> /usr/lib64/python2.7/_abcoll.py
lrwxrwxrwx   1 appname appname    62 Nov  8 04:17 _abcoll.pyc -> /usr/local/company/appname/venv/lib/python2.7/_abcoll.pyc
lrwxrwxrwx   1 appname appname    27 Nov  8 04:17 abc.py -> /usr/lib64/python2.7/abc.py
lrwxrwxrwx   1 appname appname    58 Nov  8 04:17 abc.pyc -> /usr/local/company/appname/venv/lib/python2.7/abc.pyc
lrwxrwxrwx   1 appname appname    30 Nov  8 04:17 codecs.py -> /usr/lib64/python2.7/codecs.py
lrwxrwxrwx   1 appname appname    61 Nov  8 04:17 codecs.pyc -> /usr/local/company/appname/venv/lib/python2.7/codecs.pyc
lrwxrwxrwx   1 appname appname    27 Nov  8 04:17 config -> /usr/lib64/python2.7/config
lrwxrwxrwx   1 appname appname    32 Nov  8 04:17 copy_reg.py -> /usr/lib64/python2.7/copy_reg.py
lrwxrwxrwx   1 appname appname    63 Nov  8 04:17 copy_reg.pyc -> /usr/local/company/appname/venv/lib/python2.7/copy_reg.pyc
lrwxrwxrwx   1 appname appname    60 Nov  8 04:17 distutils -> /usr/local/company/appname/venv/lib/python2.7/distutils
lrwxrwxrwx   1 appname appname    30 Nov  8 04:17 encodings -> /usr/lib64/python2.7/encodings
lrwxrwxrwx   1 appname appname    31 Nov  8 04:17 fnmatch.py -> /usr/lib64/python2.7/fnmatch.py
lrwxrwxrwx   1 appname appname    62 Nov  8 04:17 fnmatch.pyc -> /usr/local/company/appname/venv/lib/python2.7/fnmatch.pyc
lrwxrwxrwx   1 appname appname    35 Nov  8 04:17 genericpath.py -> /usr/lib64/python2.7/genericpath.py
lrwxrwxrwx   1 appname appname    66 Nov  8 04:17 genericpath.pyc -> /usr/local/company/appname/venv/lib/python2.7/genericpath.pyc
lrwxrwxrwx   1 appname appname    32 Nov  8 04:17 lib-dynload -> /usr/lib64/python2.7/lib-dynload
lrwxrwxrwx   1 appname appname    33 Nov  8 04:17 linecache.py -> /usr/lib64/python2.7/linecache.py
lrwxrwxrwx   1 appname appname    64 Nov  8 04:17 linecache.pyc -> /usr/local/company/appname/venv/lib/python2.7/linecache.pyc
lrwxrwxrwx   1 appname appname    30 Nov  8 04:17 locale.py -> /usr/lib64/python2.7/locale.py
lrwxrwxrwx   1 appname appname    61 Nov  8 04:17 locale.pyc -> /usr/local/company/appname/venv/lib/python2.7/locale.pyc
-rw-rw-r--+  1 appname appname     0 Nov  8 04:17 no-global-site-packages.txt
lrwxrwxrwx   1 appname appname    30 Nov  8 04:17 ntpath.py -> /usr/lib64/python2.7/ntpath.py
-rw-rw-r--+  1 appname appname     4 Nov  8 04:17 orig-prefix.txt
lrwxrwxrwx   1 appname appname    26 Nov  8 04:17 os.py -> /usr/lib64/python2.7/os.py
lrwxrwxrwx   1 appname appname    57 Nov  8 04:17 os.pyc -> /usr/local/company/appname/venv/lib/python2.7/os.pyc
lrwxrwxrwx   1 appname appname    33 Nov  8 04:17 posixpath.py -> /usr/lib64/python2.7/posixpath.py
lrwxrwxrwx   1 appname appname    64 Nov  8 04:17 posixpath.pyc -> /usr/local/company/appname/venv/lib/python2.7/posixpath.pyc
lrwxrwxrwx   1 appname appname    26 Nov  8 04:17 re.py -> /usr/lib64/python2.7/re.py
lrwxrwxrwx   1 appname appname    57 Nov  8 04:17 re.pyc -> /usr/local/company/appname/venv/lib/python2.7/re.pyc
drwxrwxr-x+ 40 appname appname  4096 Nov  8 04:17 site-packages
-rw-rw-r--+  1 appname appname 29021 Nov  8 04:17 site.py
-rw-rw-r--+  1 appname appname 26716 Nov  8 04:17 site.pyc
lrwxrwxrwx   1 appname appname    35 Nov  8 04:17 sre_compile.py -> /usr/lib64/python2.7/sre_compile.py
lrwxrwxrwx   1 appname appname    66 Nov  8 04:17 sre_compile.pyc -> /usr/local/company/appname/venv/lib/python2.7/sre_compile.pyc
lrwxrwxrwx   1 appname appname    37 Nov  8 04:17 sre_constants.py -> /usr/lib64/python2.7/sre_constants.py
lrwxrwxrwx   1 appname appname    68 Nov  8 04:17 sre_constants.pyc -> /usr/local/company/appname/venv/lib/python2.7/sre_constants.pyc
lrwxrwxrwx   1 appname appname    33 Nov  8 04:17 sre_parse.py -> /usr/lib64/python2.7/sre_parse.py
lrwxrwxrwx   1 appname appname    64 Nov  8 04:17 sre_parse.pyc -> /usr/local/company/appname/venv/lib/python2.7/sre_parse.pyc
lrwxrwxrwx   1 appname appname    27 Nov  8 04:17 sre.py -> /usr/lib64/python2.7/sre.py
lrwxrwxrwx   1 appname appname    28 Nov  8 04:17 stat.py -> /usr/lib64/python2.7/stat.py
lrwxrwxrwx   1 appname appname    59 Nov  8 04:17 stat.pyc -> /usr/local/company/appname/venv/lib/python2.7/stat.pyc
lrwxrwxrwx   1 appname appname    29 Nov  8 04:17 types.py -> /usr/lib64/python2.7/types.py
lrwxrwxrwx   1 appname appname    60 Nov  8 04:17 types.pyc -> /usr/local/company/appname/venv/lib/python2.7/types.pyc
lrwxrwxrwx   1 appname appname    32 Nov  8 04:17 UserDict.py -> /usr/lib64/python2.7/UserDict.py
lrwxrwxrwx   1 appname appname    63 Nov  8 04:17 UserDict.pyc -> /usr/local/company/appname/venv/lib/python2.7/UserDict.pyc
lrwxrwxrwx   1 appname appname    32 Nov  8 04:17 warnings.py -> /usr/lib64/python2.7/warnings.py
lrwxrwxrwx   1 appname appname    63 Nov  8 04:17 warnings.pyc -> /usr/local/company/appname/venv/lib/python2.7/warnings.pyc
lrwxrwxrwx   1 appname appname    35 Nov  8 04:17 _weakrefset.py -> /usr/lib64/python2.7/_weakrefset.py
lrwxrwxrwx   1 appname appname    66 Nov  8 04:17 _weakrefset.pyc -> /usr/local/company/appname/venv/lib/python2.7/_weakrefset.pyc

(I'm also interested as to why the .pyc sym links are pointing at another virtualenv when the .py links point at the system files. But I thought understanding how .pyc files can ever become sym links would be a good start.)

Answer 1

tox appears to be the culprit (or possibly one of its dependencies). The below is run on Ubuntu 18.04.

% virtualenv /tmp/venv1
Running virtualenv with interpreter /usr/bin/python2
New python executable in /tmp/venv1/bin/python2
Also creating executable in /tmp/venv1/bin/python
Installing setuptools, pkg_resources, pip, wheel...done.

% source /tmp/venv1/bin/activate

% pip install tox
Collecting tox
  Using cached https://files.pythonhosted.org/packages/d0/43/2160a300e0b77a929a980f36ac7427dcef8f4ddac7a8c21e5a8baedad828/tox-3.5.3-py2.py3-none-any.whl
Collecting filelock<4,>=3.0.0 (from tox)
Collecting six<2,>=1.0.0 (from tox)
  Using cached https://files.pythonhosted.org/packages/67/4b/141a581104b1f6397bfa78ac9d43d8ad29a7ca43ea90a2d863fe3056e86a/six-1.11.0-py2.py3-none-any.whl
Collecting virtualenv>=1.11.2 (from tox)
  Using cached https://files.pythonhosted.org/packages/7c/17/9b7b6cddfd255388b58c61e25b091047f6814183e1d63741c8df8dcd65a2/virtualenv-16.1.0-py2.py3-none-any.whl
Collecting pluggy<1,>=0.3.0 (from tox)
  Using cached https://files.pythonhosted.org/packages/1c/e7/017c262070af41fe251401cb0d0e1b7c38f656da634cd0c15604f1f30864/pluggy-0.8.0-py2.py3-none-any.whl
Requirement already satisfied: setuptools>=30.0.0 in /tmp/venv1/lib/python2.7/site-packages (from tox) (40.5.0)
Collecting py<2,>=1.4.17 (from tox)
  Using cached https://files.pythonhosted.org/packages/3e/c7/3da685ef117d42ac8d71af525208759742dd235f8094221fdaafcd3dba8f/py-1.7.0-py2.py3-none-any.whl
Collecting toml>=0.9.4 (from tox)
  Using cached https://files.pythonhosted.org/packages/a2/12/ced7105d2de62fa7c8fb5fce92cc4ce66b57c95fb875e9318dba7f8c5db0/toml-0.10.0-py2.py3-none-any.whl
Installing collected packages: filelock, six, virtualenv, pluggy, py, toml, tox
Successfully installed filelock-3.0.10 pluggy-0.8.0 py-1.7.0 six-1.11.0 toml-0.10.0 tox-3.5.3 virtualenv-16.1.0

% virtualenv /tmp/venv2
Using real prefix '/usr'
New python executable in /tmp/venv2/bin/python2
Also creating executable in /tmp/venv2/bin/python
Overwriting /tmp/venv2/lib/python2.7/distutils/__init__.py with new content
Installing setuptools, pip, wheel...
done.

% ls -l /tmp/venv2/lib/python2.7/*.pyc | head
lrwxrwxrwx 1 hdowner staff    36 Nov  8 16:57 /tmp/venv2/lib/python2.7/_abcoll.pyc -> /tmp/venv1/lib/python2.7/_abcoll.pyc
lrwxrwxrwx 1 hdowner staff    32 Nov  8 16:57 /tmp/venv2/lib/python2.7/abc.pyc -> /tmp/venv1/lib/python2.7/abc.pyc
lrwxrwxrwx 1 hdowner staff    35 Nov  8 16:57 /tmp/venv2/lib/python2.7/codecs.pyc -> /tmp/venv1/lib/python2.7/codecs.pyc
lrwxrwxrwx 1 hdowner staff    37 Nov  8 16:57 /tmp/venv2/lib/python2.7/copy_reg.pyc -> /tmp/venv1/lib/python2.7/copy_reg.pyc
lrwxrwxrwx 1 hdowner staff    36 Nov  8 16:57 /tmp/venv2/lib/python2.7/fnmatch.pyc -> /tmp/venv1/lib/python2.7/fnmatch.pyc
lrwxrwxrwx 1 hdowner staff    40 Nov  8 16:57 /tmp/venv2/lib/python2.7/genericpath.pyc -> /tmp/venv1/lib/python2.7/genericpath.pyc
lrwxrwxrwx 1 hdowner staff    38 Nov  8 16:57 /tmp/venv2/lib/python2.7/linecache.pyc -> /tmp/venv1/lib/python2.7/linecache.pyc
lrwxrwxrwx 1 hdowner staff    35 Nov  8 16:57 /tmp/venv2/lib/python2.7/locale.pyc -> /tmp/venv1/lib/python2.7/locale.pyc
lrwxrwxrwx 1 hdowner staff    31 Nov  8 16:57 /tmp/venv2/lib/python2.7/os.pyc -> /tmp/venv1/lib/python2.7/os.pyc
lrwxrwxrwx 1 hdowner staff    38 Nov  8 16:57 /tmp/venv2/lib/python2.7/posixpath.pyc -> /tmp/venv1/lib/python2.7/posixpath.pyc