Print the expected thing and got thing

Author: Jan Matějka

annotation/typed.py

@@ -466,14 +466,18 @@ def _check_argument_types(signature, *args, **kwargs):
         if not _check_type_constraint(value, annotation):
             raise TypeError('Incorrect type for "{0}"'.format(name))
 
+class IncorrectReturnType(TypeError): pass
 
 def _check_return_type(signature, return_value):
     """Check that the return value of a function matches the signature."""
     annotation = signature.return_annotation
     if annotation is EMPTY_ANNOTATION:
         annotation = AnyType
     if not _check_type_constraint(return_value, annotation):
-        raise TypeError('Incorrect return type')
+        raise IncorrectReturnType('Expected: {0!r} Got: {1!r}'.format(
+          annotation
+        , return_value
+        ))
     return return_value