* Tighten up psf/black and flake8
* Fix some tests
* Fix some E741
* Fix some E741
* updating DIRECTORY.md
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Both of the two files implemented sieve of eratosthenes.
However, there was a bug in other/finding_primes.py, and the time complexity was larger than the other.
Therefore, remove other/finding_primes.py and add doctest tomaths/sieve_of_eratosthenes.py.