title: how to input individual values in a pandas dataframe in python
body: <p>I come from an excel VBA program ming background where it is very easy to input data into </p>
  
  <p>(1) every cell in a column, 
  (2) every cell in a row, or 
  (3) a single cell e.g. B1 This can be done as an array or directly into a worksheet.</p>
  
  <p>Does a pandas dataframe, which is effectively a grid, have the ability to add an item into a specific row and column intersection?</p>
  
  <p>I know it is very good at processing data for an entire row or column with millions of rows very quickly, but can it (a pandas dataframe) have single data items put inside it.</p>
  
  <p>Think of the following diagram (columns A and B as an existing dataframe, and then I want to add the data item X to a new second column in the second row.</p>
  
  <pre><code>   A | B | C | D | 
   1| a|   |   |   |
   ------------------
   2| b| x |   |   |
   ------------------
   3| c|   |   |   |
   ------------------
   5| d|   |   |   |
   ------------------
   6| e|   |   |   |
  </code></pre>
  
  <p><strong>Can this be done?</strong></p>