The official Python Language and Library documentation can be found here:
Read the Docs is a popular community project that hosts documentation for open source software. It holds documentation for many Python modules, both popular and exotic.
Read the Docs
:program:`pydoc` is a utility that is installed when you install Python. It allows you to quickly retrieve and search for documentation from your shell. For example, if you needed a quick refresher on the :mod:`time` module, pulling up documentation would be as simple as
$ pydoc time
The above command is essentially equivalent to opening the Python REPL and running
>>> help(time)