pybcj is a bcj filter library

In data compression, BCJ, short for Branch-Call-Jump, refers to a
technique that improves the compression of machine code of executable
binaries by replacing relative branch addresses with absolute ones. This
allows a LZMA compressor to identify duplicate targets and archive
higher compression rate.

BCJ is used in 7-zip compression utility as default filter for
executable binaries.

pybcj is a python bindings with BCJ implementation by C language. The C
codes are derived from p7zip, portable 7-zip implementation.