PCPP: A C99 Preprocessor

PCPP is a pure Python implementation of a C99 preprocessor. It's designed to preprocess C and C++ source code, handling directives like `#include`, `#define`, and conditional compilation. A key use case is for processing header-only C++ libraries into single-file includes and for integration with documentation tools like Doxygen. The library is actively maintained, though with an infrequent release cadence, with the latest significant update in late 2021.