title: Declaring a TTree Branch in PyRoot
body: <p>I am trying to simply define a Root TTree using python and give it a TBranch. Sounds reasonable, right? I tried:</p>
  
  <pre><code>from ROOT import *
  myvar = int()
  mytree = TTree('mytree', 'mytree')
  tree.Branch('myvar', AddressOf(myvar), 'myvar/I')
  exit(0)
  </code></pre>
  
  <p>and this crashes with the error:</p>
  
  <pre><code>ValueError: invalid argument for AddressOf().
  </code></pre>
  
  <p>I suspected that perhaps the argument of AddressOf() needs to be a Root type like Int_t, but I didn't think python data types needed to be made explicit--and furthermore I couldn't figure out how to force the data type of of int to be Int_t. Finally, if you do the same exact thing except replace the 'int' with 'TString' and the '/I' with '/S', things do not crash. Any suggestion is appreciated.</p>