Jedi.el is a Python auto-completion package for Emacs. It aims at helping your Python coding in a non-destructive way. It also helps you to find information about Python objects, such as docstring, function arguments and code location.
For more info, read documentation. If you are using developmental version installed via el-get or MELPA, read the developmental version. If you are using released version installed via Marmalade, read the released version.
Auto-completion using Jedi.el. See more screenshots here.