title: Can't seem to shorten decimal numbers of my Pandas column
body: <p>So I have a df column which I created by taking an average of three other columns</p>
  
  <p><code>df['Avg_Grade'] = df.loc[:,'G1':'G3'].mean(axis =1)</code></p>
  
  <p>The series looks like this (just a sample)</p>
  
  <pre><code>   Avg_Grade  
  0   5.666667  
  1   5.333333  
  2   8.333333  
  3  14.666667  
  4   8.666667  
  </code></pre>
  
  <p>I'm trying to truncate the output to show something like</p>
  
  <pre><code> 0   5.67 (5.66 is also fine)
   1   5.33  
   2   8.33  
   3   14.67  
   4   8.67
  </code></pre>
  
  <p>I've played around with the module<code>Decimal</code> with the following code, but I'm getting an error. </p>
  
  <pre><code>from decimal import *
  getcontext().prec = 4
  
  
  df['Avg_Grade'] = Decimal(df.loc[:,'G1':'G3'].mean(axis =1))
  
  
   Traceback (most recent call last):
    File "&lt;pyshell#409&gt;", line 1, in &lt;module&gt;
      df['Avg_Grade'] = Decimal(df.loc[:,'G1':'G3'].mean(axis =1))
    File "C:\Python27\lib\decimal.py", line 657, in __new__
      raise TypeError("Cannot convert %r to Decimal" % value)
  TypeError: Cannot convert 0       5.666667
  </code></pre>