Merge pull request #216 from goodfeli/missing_input_error_message

theano/gof/env.py

@@ -5,6 +5,7 @@ from copy import copy
 import graph
 import utils
 import toolbox
+from theano import config
 
 
 class InconsistencyError(Exception):
@@ -232,6 +233,63 @@ class Env(utils.object2):
                     if hasattr(r, 'env') and r.env is not self:
                         raise Exception("%s is already owned by another env" % r)
                     if r.owner is None and not isinstance(r, graph.Value) and r not in self.inputs:
+
+                        #Verbose error message
+                        #Show a complete chain of variables from the missing input to an output
+                        if config.exception_verbosity == 'high':
+
+                            def find_path_to(output_var, input_var):
+                                """ Returns a list of each variable on a (not necessarily unique)
+                                    path from input_var to output_var, where each variable in the
+                                    list has the preceding variable as one of its inputs.
+                                    Returns None if no path exists"""
+
+                                #If output and input are the same we have a singleton path
+                                if output_var is input_var:
+                                    return [output_var]
+
+                                #If output has no inputs then there is no path
+                                owner = output_var.owner
+
+                                if owner is None:
+                                    return None
+
+                                #If input_var is an input to the output node, there is a
+                                #simple two element path
+                                inputs = owner.inputs
+
+                                if input_var in inputs:
+                                    return [input_var, output_var]
+
+                                #Otherwise we must recurse by searching for a path to one
+                                #of our inputs, then appending the output to that path
+                                for ipt in inputs:
+                                    path = find_path_to(ipt, input_var)
+
+                                    if path is not None:
+                                        path.append(output_var)
+
+                                        return path
+
+                                #Since none of the above methods returned a path, there is none
+                                return None
+
+                            #Try different outputs until we find one that has a path to the missing input
+                            for output in self.outputs:
+                                path = find_path_to(output, r)
+
+                                if path is not None:
+                                    break
+
+                            #if there is no path then r isn't really a graph input so we shouldn't be running error
+                            #handler code in the first place
+                            assert path is not None
+
+                            raise TypeError('A variable that is an input to the graph was neither provided as an '
+                                    'input to the function nor given a value. A chain of variables leading from '
+                                    'this input to an output is '+str(path)+'. This chain may not be unique')
+
+                        #Standard error message
                         raise TypeError("An input of the graph, used to compute "+str(node)+", was not provided and not given a value", r)
 
         for node in new_nodes: