What is the difference between libraries with the "_" prefix symbol and libraries without it?

Question

Python

What is the difference between these (and not only) libs from each other?

Answer 1

According to PEP 399 , the modules with the prefix are written in C (or just "speedy" versions written in a language other than Python).
As for modules not from the standard libraries, the prefix can have the same meaning as everywhere in Python - meaning that the given library should not be imported directly, i.e. is private.

Answer 2

https://www.python.org/dev/peps/pep-0399/#details