py-yapf.el

Provides commands, which use the external “yapf” tool to tidy up the current buffer according to Python’s PEP8.

$ pip install git+https://github.com/google/yapf.git
$ wget https://raw.githubusercontent.com/paetzke/py-yapf.el/master/py-yapf.el \
       -O /your/path/py-yapf.el

You can also install py-yapf with MELPA:

M-x package-install RET
py-yapf RET

Add the before-save-hook to your ~/.emacs

(add-to-list 'load-path "/your/path/")
(require 'py-yapf)
(add-hook 'before-save-hook 'py-yapf-before-save)

Now every time you save your Python file yapf will be executed on the current buffer.