问题
I've installed python on mac with homebrew. Some tools (pipenv for example) have some troubles because they try to write to /lib/python3.7/site-packages/
, not permitted under mac. After some investigation I found that they start a new python interpreter found in sys.executable
that is effectively inconsistent with the python path installed by homebrew.
$ which python
/usr/local/bin/python
$ python -c "import sys; print(sys.executable)"
/usr/local/opt/python/bin/python3.7
I would expect that these path points to the same binary, why is it not so? How can I control sys.executable
?
回答1:
It is determined at runtime (by the calculate_program_full_path() function in Module/getpath.c, to be exact. It is usually based of the argv[0]
value that the OS passed in.
You can set an alternative value by setting the PYTHONEXECUTABLE environment variable.
However, on homebrew builds, a bit more is going on. Homebrew forces the issue and sets sys.executable
directly in a sitecustomize.py module generated at install time:
$ tail -n2 /usr/local/Cellar/python/3.7.0/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/sitecustomize.py
# Set the sys.executable to use the opt_prefix
sys.executable = '/usr/local/opt/python/bin/python3.7'
This blithely ignores PYTHONEXECUTABLE
even if set.
So what is going on, why does homebrew clobber sys.executable
?
Homebrew Python is a MacOS framework build, so you can run GUI apps with this Python binary. A binary inside a framework bundle is placed under very strict requirements by Apple as to what you can do with it, including what the executable name is allowed to be set to. To work around these the framework binary is actually a wrapper ) that translates takes to a better path, sets the __PYVENV_LAUNCHER__
environment variable and launches the actual python binary located at Resources/Python.app/Contents/MacOS/Python
, which then uses the __PYVENV_LAUNCHER__
environment variable to inform sys.executable
.
The path the wrapper sets has any symlinks in the directory name resolved. Since homebrew makes /usr/local/opt/python
a symlink to a specific Python bottle directory, running /usr/local/opt/python/bin/python3
results in sys.executable
being set to the linked bottle path:
$ /usr/local/opt/python/bin/python3 -S -c 'import sys; print(sys.executable)'
/usr/local/Cellar/python/3.7.0/bin/python3
which defeats the purpose of the symlink, and can lead to broken pip-installed scripts each time homebrew makes a minor version update to the Python formula.
I'd like for homebrew to at least check if PYTHONEXECUTABLE
is set here. You can force the issue yourself by just setting sys.executable
directly:
import os, sys
if 'PYTHONEXECUTABLE' in os.environ and :
sys.executable = os.environ['PYTHONEXECUTABLE']
I've opened a report to request the homebrew Python formula checks for PYTHONEXECUTABLE and included a suggested fix. The fix was landed on November 28, 2018, so just an update of your Python packages should get you the new version and make Homebrew Python honour PYTHONEXECUTABLE
once again.
来源:https://stackoverflow.com/questions/53189145/how-does-sys-executable-determine-the-interpreter-path