tensor.basic - Changed E_grad from a string to an Exception subclass.

theano/tensor/basic.py

@@ -4004,7 +4004,19 @@ def verify_grad(op, pt, n_tests=2, rng=None, eps=None, tol=None, mode=None, cast
 
         max_err, max_err_pos = num_grad.max_err(analytic_grad)
         if  max_err > tol:
-            raise Exception(verify_grad.E_grad, (max_err, tol, max_err_pos))
+            raise verify_grad.E_grad(tol, num_grad, analytic_grad)
+
+class GradientError(Exception):
+    """This error is raised when a gradient is calculated, but incorrect."""
+    def __init__(self, tol, num_grad, analytic_grad):
+        self.num_grad = num_grad
+        self.analytic_grad = analytic_grad
+        self.tol = tol
+    def __str__(self):
+        max_errs = [numpy.max(e) for e in self.num_grad.abs_rel_errors(self.analytic_grad)]
+        return "GradientError: numeric gradient and analytic gradient differ than %f (%s)" %(
+                self.tol, max_errs)
+    def abs_rel_errors(self):
+        return self.num_grad.abs_rel_errors(self.analytic_grad)
 
-verify_grad.E_grad = 'gradient error exceeded tolerance'
-"""This error is raised when a gradient is calculated, but incorrect."""
+verify_grad.E_grad = GradientError