title: df.query while using pandas in python produces empty results
body: <p>I am learning how to manipulate data using pandas in python. I got the following script:</p>
  
  <pre><code>import pandas as pd
  
  df = pd.read_table( "t.txt" )    #read in the file
  df.columns = [x.strip() for x in df.columns]   #strip spaces in headers
  df = df.query('TLD == ".biz"')     #select the rows where TLD == ".biz"
  df.to_csv('t.txt', sep='\t')  #write the output to a tab-separated file
  </code></pre>
  
  <p>but the output file has no records, headers only. When I check using</p>
  
  <pre><code>print.df
  </code></pre>
  
  <p>prior to the selection, the output is:</p>
  
  <pre><code>             TLD  Length                                              Words  \
  0       .biz           5                                                ...   
  1       .biz           4                                                ...   
  2       .biz           5                                                ...   
  3       .biz           5                                                ...   
  4       .biz           3                                                ...   
  5       .biz           3                                                ...   
  6       .biz           6                                                ...   
  </code></pre>
  
  <p>So I know the column TLD has rows with the .biz values. I also tried :</p>
  
  <pre><code>&gt;&gt;&gt; print(df.loc[df['TLD'] == '.biz'])
  </code></pre>
  
  <p>but the results is</p>
  
  <pre><code>Empty DataFrame
  </code></pre>
  
  <p>With list of my columns</p>
  
  <p>What am I doing wrong please?</p>