/usr/share/system-config-printer/HIG.py is in system-config-printer-gnome 1.5.7+20160212-0ubuntu2.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 3 4 | PAD_SMALL = 3
PAD_NORMAL = 6
PAD_BIG = 12
PAD_LARGE = 18
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