title: pandas 0.23.1 AttributeError: 'module' object has no attribute 'rolling'
body: <pre><code>import pandas as pd
  import numpy as np
  from pandas import *
  
  print (pd.__version__)
  df = pd.DataFrame({'key1':['a','a','b','b','a'],
                 'key2':['one','two','one','two','one'],
                 'data1':np.nan,
                 'data2':np.random.randn(5)})
  
  df = pd.rolling(df[['data1','data2']],window = 3)
  print (df)
  </code></pre>
  
  <p>return:</p>
  
  <pre><code>0.23.1
  Traceback (most recent call last):
    File "jj.py", line 33, in &lt;module&gt;
      df = pd.rolling(df[['data1','data2']],window = 3)
  AttributeError: 'module' object has no attribute 'rolling'
  </code></pre>
  
  <p>I try python2 and python3 at my computer, but all failed when I use rolling()</p>