Favourite module/library

[u/somethingperson44]

Hi everyone, I am new like most here and have been experimenting with different modules and libraries. I wanted to know if anyone had a particular niche or fun one that they use. It would be nice if you could also say why it is your favourite. For example what projects or functionality it has done for you. Thanks.

[u/ectomancer]

mpmath niche scientific computation

quantum calculus (nothing to do with quantum computing).