Link to
The Python Standard Library.
One the best online
Python 3 Module of the Week.
Also a book
The Python 3 Standard Library by Example massive 1456 pages.
Starting to get a little old now,but still good
Python Essential Reference.
As a advice learn to explore modules yourself live,here will a better REPL like
ptpython or
IPython helps.
A good editors with autocompletion/IntelliSense like Vs Code or PyChram also helps.
It's not possible to remember all this stuff.
Here a image with pypython and cmder,see that all method of lxml show up automatically,
then it's much more easy to choose and test out stuff.
There are modules in Standard Library that i mean there are not worth spending any time on like urllib,here have
Requests taken over.
For me personalty also all HTML/XML parsing stuff in Standard Library,here is BeautifulSoup/lxml better.