Merge pull request #75 from delallea/tensor_cast_error

theano/compile/function_module.py

@@ -537,7 +537,8 @@ class Function(object):
                     if self.name:
                         function_name += 'with name "'+self.name+'" '
                     #end if
-                    e.args = tuple(list(e.args)+["Bad input argument to "+function_name+" at index %d" % i])
+                    e.args = tuple(["Bad input argument to " + function_name +
+                                    " at index %d" % i] + list(e.args))
                     raise
                 #end except
             #end if

theano/tensor/basic.py

@@ -533,6 +533,13 @@ class TensorType(Type):
         This function is not meant to be called in user code.  It is for
         `Linker` instances to use when running a compiled graph.
         """
+        # Explicit error message when one accidentally uses a Variable as
+        # input (typical mistake, especially with shared variables).
+        if isinstance(data, Variable):
+            raise TypeError(
+                    'Expected an array-like object, but found a Variable: '
+                    'maybe you are trying to call a function on a (possibly '
+                    'shared) variable instead of a numeric array?')
         if (type(data) is numpy.ndarray) and (data.dtype is self.numpy_dtype):
             pass # fall through to ndim check
         elif strict: