Codex Africanus presents radio astronomy algorithms to the user as modular functions accepting NumPy inputs and producing NumPy outputs. Internally, it uses Numba to accelerate these codes and Dask to parallelize and distribute them. The library contains functions for plotting convolution filters and tapers associated with convolution filters and can compute the discretised direct Fourier transform (DFT) for an ideal interferometer. Codex Africanus has routines for gridding or degridding complex visibilities onto or from an image, includes deconvolution algorithms and coordinate transforms, and many other functions.