Bug report

Bug summary

If matplotlib is run in an environment without a writable home directory, a very confusing error message is printed in which the configdir and the tempdir are interchanged.

Code for reproduction

1. In Linux, create a usersomeone with no home directory.

2. Run Python with a command like

   sudo -u someone python3

3. In the Python shell, typeimport matplotlib

Actual outcome

Matplotlib created a temporary config/cache directory at /root/.config/matplotlib because the default path (/tmp/matplotlib-9yoi7m8l) is not a writable directory; it is highly recommended to set the MPLCONFIGDIR environment variable to a writable directory, in particular to speed up the import of Matplotlib and to better support multiprocessing.

Expected outcome

Matplotlib created a temporary config/cache directory at /tmp/matplotlib-9yoi7m8l because the default path (/root/.config/matplotlib) is not a writable directory; it is highly recommended to set the MPLCONFIGDIR environment variable to a writable directory, in particular to speed up the import of Matplotlib and to better support multiprocessing.

Matplotlib version

• Operating system: Ubuntu 18.04
• Matplotlib version: 3.3.0
• Matplotlib backend (print(matplotlib.get_backend())): agg
• Python version: 3.9.0b4
• Jupyter version (if applicable): N/A
• Other libraries: N/A

Matplotlib was compiled from source. The error is at line 482 in__init__.py at the root level in the source tree. The parameters are the wrong way round.