Integrate pep8 for Python code style checking

[wangkuiyi]

https://pypi.python.org/pypi/pep8

[QiJune]

I find a useful open source tool created by google, yapf https://github.com/google/yapf
pip install yapf will install yapf tool.
This tool provides 4 based style to choose: pep8, google, facebook and chromium.
The style can be find in this link. https://github.com/google/yapf/blob/master/yapf/yapflib/style.py

I make some python code formatting test on currently code on github
Here is a .style.yapf config file created in paddle directory:

[style]
based_on_style = google
indent_width = 4
spaces_before_comment = 4
split_before_logical_operator = true

After run yapf -r -i python/, the python code will be formatted.
But, it brings so much diff and changes our python code format.
Should we format the code right now, or just add a yapf config file?

[reyoung]

basically done, closed