title: Manually set the keys in Pandas DataFrame built with read_csv
body: <p>I have a .tsv file dataset, and I transformed it into a DataFrame using Pandas.
  Imagine that my_tsv_file was something like:</p>
  
  <pre><code>A Apple
  B Orange
  C Pear
  </code></pre>
  
  <p>To build the DataFrame I used:</p>
  
  <pre><code>df = pandas.read_csv(my_tsv_file, sep='\t')
  </code></pre>
  
  <p>Now, the first row of my_tsv_file was originally a row part of the data, but it has been transformed to the "key row" in the new DataFrame. So now the Dataframe is something like:</p>
  
  <pre><code>      A Apple
     0  B Orange
     1  C Pear
  </code></pre>
  
  <p>As "A" and "Apple" were keys, when they actually are not. I would like to add the correct "key row", in order to obtain something like:</p>
  
  <pre><code>      ID Fruit
     0  A  Apple
     1  B  Orange
     2  C  Pear
  </code></pre>
  
  <p>How can I achieve this?
  I can't modify the original .tsv file.
  Please remind that I am at the very beginning with Python and Pandas.</p>