If you’ve encountered a warning like this while running a WSGI application with Apache and mod_wsgi
:
UserWarning: NumPy was imported from a Python sub-interpreter but NumPy does not properly support sub-interpreters. This will likely work for most users but might cause hard to track down issues or subtle bugs. A common user of the rare sub-interpreter feature is wsgi which also allows single-interpreter mode.
You’re not alone. This warning indicates that NumPy was imported in a sub-interpreter, which can lead to subtle bugs and hard-to-track-down issues. Fortunately, there’s a straightforward solution.
Why This Happens
Apache’s mod_wsgi
can run WSGI applications in sub-interpreters to isolate different applications. However, some libraries, like NumPy, do not fully support this feature. Running NumPy in a sub-interpreter can lead to unpredictable behavior and warnings.
Solution: Use Single-Interpreter Mode
To prevent these issues, configure mod_wsgi
to run in single-interpreter mode. This forces your application to run in the main interpreter, avoiding the problems associated with sub-interpreters.
Here’s how you can do it:
Step-by-Step Guide
- Edit Your Apache Configuration:Open your Apache configuration file (e.g.,
000-default.conf
or your specific virtual host configuration file) and add theWSGIApplicationGroup
directive.
<VirtualHost *:80>
ServerName yourdomain.com
DocumentRoot /path/to/your/project
WSGIDaemonProcess your_app_name python-path=/path/to/your/project python-home=/path/to/your/virtualenv
WSGIProcessGroup your_app_name
WSGIScriptAlias / /path/to/your/project/wsgi.py
# Add this line to force the use of the main interpreter
WSGIApplicationGroup %{GLOBAL}
<Directory /path/to/your/project>
<Files wsgi.py>
Require all granted
</Files>
</Directory>
ErrorLog ${APACHE_LOG_DIR}/error.log
CustomLog ${APACHE_LOG_DIR}/access.log combined
</VirtualHost>
Explanation:
WSGIApplicationGroup %{GLOBAL}
: This directive tellsmod_wsgi
to run the WSGI application in the main interpreter of the process, avoiding sub-interpreters.
Restart Apache:
After making the changes, restart Apache to apply the new settings.
sudo systemctl restart apache2
or
sudo systemctl restart httpd
Additional Tips
- Monitor Logs: Keep an eye on your logs to ensure that the warning is gone and no other issues arise.
- Check for Other Libraries: If you use other libraries that might not support sub-interpreters, running in single-interpreter mode should help with those as well.
Conclusion
By setting WSGIApplicationGroup %{GLOBAL}
, you can avoid the NumPy warning and prevent potential issues associated with sub-interpreters in your WSGI application. This simple configuration change ensures that your application runs smoothly and reliably.
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I hope this guide helps you resolve the NumPy sub-interpreter warning in your WSGI applications. If you have any questions or need further assistance, please leave a comment below!
Amit Mittal