title: Why the where clause does not work in the pandas?
body: <p>Given that, I have 2 datasets as below:</p>
  
  <pre><code>import pandas as pd
  import numpy as np
  
  dict1 = {
      "A" : range(1,6),
      "B": np.random.randint(1,10,5)
  }
  
  dt1 = pd.DataFrame(dict1)
  
  dict2 = {
      "A" : range(1,6),
      "K" : np.random.randint(3,8,5),
      "Size of Sessile in Words": ["Small","Small","Medium","Large","Medium",]
  }
  
  dt2 = pd.DataFrame(dict2)
  </code></pre>
  
  <p>I am trying to <code>join</code> these 2 dataframes but also use a <code>Where</code> clause as well:</p>
  
  <pre><code>size = "Small"
  dt = dt1.merge(dt2, on='A').query('"Size of Sessile in Words" == {size}'.format(size) )
  </code></pre>
  
  <p>But, it complains with:</p>
  
  <pre><code>KeyError: 'size'
  </code></pre>
  
  <p>What is the problem?</p>