title: Pandas dataframe column of floats to percentage style error
body: <p>I am trying to convert a pandas dataframe column of floats to percentage style</p>
  
  <pre><code>C
  0.9977
  0.1234
  1.000
  ..
  </code></pre>
  
  <p>to</p>
  
  <pre><code>C
  99.77%
  12.34%
  100%
  ...
  </code></pre>
  
  <p>To do this, I am doing:</p>
  
  <pre><code>df['C'] = df['C'].map(lambda n: '{:.2%}'.format(n))
  </code></pre>
  
  <p>but I am getting the following error:</p>
  
  <pre><code>ValueError: Unknown format code '%' for object of type 'str'
  </code></pre>
  
  <p>I also tried <code>'{:,.2%}'</code> with the same error...</p>
  
  <p>What I am doing wrong?</p>