/usr/lib/python3.5/test/data/README is in libpython3.5-testsuite 3.5.1-10.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | This empty directory serves as destination for temporary files
created by some tests, in particular, the test_codecmaps_* tests.
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