Step-by-step guide
To test the much faster CFFI API level, out-of-line mode you need the ecCodes header files. Then you need to clone the repo in the same folder as your ecCodes source tree, make a pip development install and custom compile the binary bindings:
$ git clone https://github.com/ecmwf/eccodes-python
$ cd eccodes-python
$ pip install -e .
$ cp {ECCODES_DIR}/include/*.h {ECCODES_DIR}/include/python3.x/
$ python builder.py