title: Getting value of a tensor variable in Theano
body: <p>I am a noob at Theano - so please be patient.</p>
  
  <p>I'm trying to implement gradient clipping for a project. A code snippet is as below :</p>
  
  <pre><code>grads = tensor.grad(cost, wrt=itemlist(tparams))
  
  grad_norm = tensor.sqrt(sum(map(lambda x: tensor.sqr(x).sum(), grads)))
  grad_norm = tensor.sqrt(grad_norm)
  print grad_norm.eval()
  </code></pre>
  
  <p>The error I receive is as follows : </p>
  
  <p><code>
  theano.gof.fg.MissingInputError: ("An input of the graph, used to    compute Shape(x), was not provided and not given a value.Use the Theano flag exception_verbosity='high',for more information on this error.", x)
  </code>
  Please advice.</p>