title: Pandas query function not working with spaces in column names
body: <p>I have a dataframe with spaces in column names. I am trying to use <code>query</code> method to get the results. It is working fine with 'c' column but getting error for 'a b'</p>
  
  <pre><code>import pandas as pd
  a = pd.DataFrame(columns=["a b", "c"])
  a["a b"] = [1,2,3,4]
  a["c"] = [5,6,7,8]
  a.query('a b==5')
  </code></pre>
  
  <p>For this I am getting this error:</p>
  
  <pre><code>a b ==5
    ^
  SyntaxError: invalid syntax
  </code></pre>
  
  <p>I don't want to fill up space with other characters like '_' etc. </p>
  
  <p>There is one hack using pandasql to put variable name inside brackets example: <strong>[a b]</strong></p>