Jedi is an autocompletion library for Python.
From the Jedi website:
Jedi is an autocompletion tool for Python that can be used in IDEs/editors. Jedi works. Jedi is fast. It understands all of the basic Python syntax elements including many builtin functions.
Additionaly, Jedi suports two different goto functions and has support for renaming as well as Pydoc support and some other IDE features.
To use Jedi, the library must be installed. Most users also install an editor plugin.
Plugins exist for Vim, Emacs, Sublime Text, and SynWrite.