This code accompanies the work published in the paper by Z. Gao, Z. Vlah, A. Challinor, Flat-sky angular power spectra revisited Published in: JCAP 02 (2024) 003 • e-Print: 2307.13768 (https://arxiv.org/abs/2307.13768). The code contains Python scripts for calculating the results presented in the paper. Major functioning scripts are: Decomposition.py Cosmology.py Calculation.py Calculation_RSD.py The application of these scripts is described in the Jupyter/Python notebook example.ipynb The full-sky angular power spectra are pre-calculated and stored in: ./Full-sky/ (.txt type for clustering, .npy type for RSD) Note that all the angular power spectra are calculated based on the power spectrum given in /cosmo_params/pk_camb_planck18.txt Required packages are numpy, scipy, mpmath, pyCAMB, and CLASS (all the dependencies are publically available). The choice of cosmology-related functions could be replaced with anything users are familiar with. All the flat-sky calculations are based on the Gaussian window function. In practice, as long as you have two mesh grids of targeting sources on Windows, Growth factors... you can use power_calc_sampling-like functions in Calculation.py and Calculation_RSD.py to calculate. In the interest of open and reproducible research, the code is also available on GitHub (https://github.com/GZCPhysics/BeyondLimber)