@free
```
DataFrame.pct_change(periods=1, fill_method='pad', limit=None, freq=None, **kwargs)
Percent change over given number of periods.
```
具体可以查看pandas的文档
[pandas.DataFrame.pct_change][1]
[1]: http://pandas.pydata.org/pandas-docs/version/0.16.2/generated/pandas.DataFrame.pct_change.html#pandas.DataFrame.pct_change
雪球
