title: working on simple HTML table columns parsing
body: <p>I am working on HTML tables using python.   </p>
  
  <p>I want to know that how can i fetch different column values using lxml?</p>
  
  <p>HTML table :</p>
  
  <pre><code>&lt;table border="1"&gt;
  &lt;tr&gt;
  &lt;td&gt;Header_1&lt;/td&gt;
  &lt;td&gt;Header_2&lt;/td&gt;
  &lt;td&gt;Header_3&lt;/td&gt;
  &lt;td&gt;Header_4&lt;/td&gt;
  &lt;/tr&gt;
  &lt;tr&gt;
  &lt;td&gt;row 1_cell 1&lt;/td&gt;
  &lt;td&gt;row 1_cell 2&lt;/td&gt;
  &lt;td&gt;row 1_cell 3&lt;/td&gt;
  &lt;td&gt;row 1_cell 4&lt;/td&gt;
  &lt;/tr&gt;
  &lt;tr&gt;
  &lt;td&gt;row 2_cell 1&lt;/td&gt;
  &lt;td&gt;row 2_cell 2&lt;/td&gt;
  &lt;td&gt;row 1_cell 3&lt;/td&gt;
  &lt;td&gt;row 1_cell 4&lt;/td&gt;
  &lt;/tr&gt;
  &lt;tr&gt;
  &lt;td&gt;row 3_cell 1&lt;/td&gt;
  &lt;td&gt;row 3_cell 2&lt;/td&gt;
  &lt;td&gt;row 1_cell 3&lt;/td&gt;
  &lt;td&gt;row 1_cell 4&lt;/td&gt;
  &lt;/tr&gt;
  &lt;tr&gt;
  &lt;td&gt;row 4_cell 1&lt;/td&gt;
  &lt;td&gt;row 4_cell 2&lt;/td&gt;
  &lt;td&gt;row 1_cell 3&lt;/td&gt;
  &lt;td&gt;row 1_cell 4&lt;/td&gt;
  &lt;/tr&gt;
  &lt;/table&gt;    
  </code></pre>
  
  <p>and I am looking to get output as : </p>
  
  <pre><code>[
  [
  ('Header_1', 'Header_2'),
  ('row 1_cell 1', 'row 1_cell 2'),
  ('row 2_cell 1', 'row 2_cell 2'),
  ('row 3_cell 1', 'row 3_cell 2'),
  ('row 4_cell 1', 'row 4_cell 2')
  ],
  [
  ('Header_1', 'Header_3'),
  ('row 1_cell 1', 'row 1_cell 3'),
  ('row 2_cell 1', 'row 2_cell 3'),
  ('row 3_cell 1', 'row 3_cell 2'),
  ('row 4_cell 1', 'row 4_cell 3')
  ]
  ]
  </code></pre>
  
  <p>how can i fetch such different column and their values?</p>