## Notes Custom [[Pandas]] very easily will work bad when using multithreading (which is the default mode of [[Dask]] when using dask dataframes). In theory, Pandas, as well as [[NumPy]], releases the GIL under certain circumnstances... but in our case (for example, as soon as you write a custom apply), that will not be the case and multithreading will perform even worse than single-threaded. Thus, it is more interesting to use multiprocessing mode with only one thread per process.