/usr/lib/python3/dist-packages/matplotlib/tests/test_rcparams.rc is in python3-matplotlib 1.3.1-1ubuntu5.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 | # this file is used by the tests in test_rcparams.py
lines.linewidth: 33
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