title: Evaluate contents of object
body: <p>I'm trying to create a spreadsheet application using Python3 and am having difficulty setting it up to be able to do cross-cell functions, such as:</p>
  
  <pre><code>a0+2
  </code></pre>
  
  <p>where a0 is a tkinter textbox containing a string. I have made a dictionary mapping each address (a0, a1, a2, etc) to the cell object, but am not sure whether to make the program parse the string looking for an address string, or whether there is some very neat <code>eval()</code> trick. I have tried using <code>eval()</code>, but I keep getting an error</p>
  
  <p><code>TypeError: globals must be a real dict; try eval(expr, {}, mapping)</code></p>
  
  <p>No matter where I put the dictionary, or even if I tried to use a global cast. Any help would be appreciated.</p>