Bug1085

ChangeLog

@@ -76,6 +76,10 @@ What's New in Pylint 1.8?
       After a change message is correctly not emitted for this case.
       Close #1559
 
+    * Fix a false positive ``useless-super-delegation`` message when
+      parameters default values are different from those used in the base class.
+      Close #1085
+
 What's New in Pylint 1.7.1?
 =========================
 

pylint/checkers/classes.py

@@ -133,6 +133,24 @@ def _positional_parameters(method):
         positional = positional[1:]
     return positional
 
+def _has_different_parameters_default_value(original, overridden):
+    """
+    Return True if one of the overridden arguments has a default
+    value different from the default value of the original argument
+    """
+    orig_name = [param.name for param in original.args]
+    for param_name in orig_name:
+        try:
+            orig_default = original.default_value(param_name).value
+        except astroid.exceptions.NoDefault:
+            orig_default = None
+        try:
+            over_default = overridden.default_value(param_name).value
+            if orig_default != over_default:
+                return True
+        except astroid.exceptions.NoDefault:
+            pass
+    return False
 
 def _has_different_parameters(original, overridden, dummy_parameter_regex):
     zipped = six.moves.zip_longest(original, overridden)
@@ -197,7 +215,6 @@ def _different_parameters(original, overridden, dummy_parameter_regex):
         different_kwonly
     ))
 
-
 def _is_invalid_base_class(cls):
     return cls.name in INVALID_BASE_CLASSES and is_builtin_object(cls)
 
@@ -705,7 +722,8 @@ def _check_useless_super_delegation(self, function):
         nothing additional whatsoever than not implementing the method at all.
         If the method uses super() to delegate an operation to the rest of the MRO,
         and if the method called is the same as the current one, the arguments
-        passed to super() are the same as the parameters that were passed to
+        passed to super(), including their default value,
+        are the same as the parameters that were passed to
         this method, then the method could be removed altogether, by letting
         other implementation to take precedence.
         '''
@@ -757,6 +775,11 @@ def _check_useless_super_delegation(self, function):
             return
         if super_call.type.name != current_scope.name:
             return
+
+        # Detect if the method has argument with default value that is
+        # different from the one used in the base method
+        if self._check_different_default_values_in_overridden_method(function):
+            return
 
         # Detect if the parameters are the same as the call's arguments.
         params = _signature_from_arguments(function.args)
@@ -765,6 +788,34 @@ def _check_useless_super_delegation(self, function):
             self.add_message('useless-super-delegation', node=function,
                              args=(function.name, ))
 
+    @staticmethod
+    def _check_different_default_values_in_overridden_method(function):
+        """
+        Check if the parameters default values in overridden methods are
+        different from those in the base class
+        """
+        klass = function.parent.frame()
+        for overridden in klass.local_attr_ancestors(function.name):
+            # get astroid for the searched method
+            try:
+                meth_node = overridden[function.name]
+            except KeyError:
+                # we have found the method but it's not in the local
+                # dictionary.
+                # This may happen with astroid build from living objects
+                continue
+            if not isinstance(meth_node, astroid.FunctionDef):
+                continue
+            instance = klass.instantiate_class()
+            method1 = function_to_method(function, instance)
+            refmethod = function_to_method(meth_node, instance)
+            # Don't care about functions with unknown argument (builtins).
+            if method1.args.args is None or refmethod.args.args is None:
+                continue
+            if _has_different_parameters_default_value(refmethod.args, method1.args):
+                return True
+        return False
+
     def _check_slots(self, node):
         if '__slots__' not in node.locals:
             return
@@ -1229,7 +1280,6 @@ def _check_signature(self, method1, refmethod, class_type, cls):
                 if (isinstance(decorator, astroid.Attribute) and
                         decorator.attrname == 'setter'):
                     return
-
         if _different_parameters(
                 refmethod, method1,
                 dummy_parameter_regex=self._dummy_rgx):

pylint/test/functional/useless_super_delegation.py

@@ -10,6 +10,12 @@ class Base(object):
     def something(self):
         pass
 
+    def with_default_argument(self, first, default_arg="default"):
+        pass
+
+    def without_default_argument(self, first, second):
+        pass
+
 
 class NotUselessSuper(Base):
 
@@ -92,6 +98,13 @@ def extraneous_positional_args(self, **args):
         super(NotUselessSuper, self).extraneous_positional_args(
             1, 2, **args)
 
+    def with_default_argument(self, first, default_arg="other"):
+        # Not useless because the default_arg is different from the one in the base class
+        super(NotUselessSuper, self).with_default_argument(first, default_arg)
+
+    def without_default_argument(self, first, second=True):
+        # Not useless because in the base class there is not default value for second argument
+        super(NotUselessSuper, self).without_default_argument(first, second)
 
 class UselessSuper(Base):
 
@@ -116,6 +129,13 @@ def equivalent_params_5(self, first, *args): # [useless-super-delegation]
     def equivalent_params_6(self, first, *args, **kwargs): # [useless-super-delegation]
         return super(UselessSuper, self).equivalent_params_6(first, *args, **kwargs)
 
+    def with_default_argument(self, first, default_arg="default"): # [useless-super-delegation]
+        # useless because the default value here is the same as in the base class
+        return super(UselessSuper, self).with_default_argument(first, default_arg)
+
+    def without_default_argument(self, first, second): # [useless-super-delegation]
+        return super(UselessSuper, self).without_default_argument(first, second)
+
     def __init__(self): # [useless-super-delegation]
         super(UselessSuper, self).__init__()
 

pylint/test/functional/useless_super_delegation.txt

@@ -1,8 +1,10 @@
-useless-super-delegation:98:UselessSuper.equivalent_params:Useless super delegation in method 'equivalent_params'
-useless-super-delegation:101:UselessSuper.equivalent_params_1:Useless super delegation in method 'equivalent_params_1'
-useless-super-delegation:104:UselessSuper.equivalent_params_2:Useless super delegation in method 'equivalent_params_2'
-useless-super-delegation:107:UselessSuper.equivalent_params_3:Useless super delegation in method 'equivalent_params_3'
-useless-super-delegation:110:UselessSuper.equivalent_params_4:Useless super delegation in method 'equivalent_params_4'
-useless-super-delegation:113:UselessSuper.equivalent_params_5:Useless super delegation in method 'equivalent_params_5'
-useless-super-delegation:116:UselessSuper.equivalent_params_6:Useless super delegation in method 'equivalent_params_6'
-useless-super-delegation:119:UselessSuper.__init__:Useless super delegation in method '__init__'
+useless-super-delegation:111:UselessSuper.equivalent_params:Useless super delegation in method 'equivalent_params'
+useless-super-delegation:114:UselessSuper.equivalent_params_1:Useless super delegation in method 'equivalent_params_1'
+useless-super-delegation:117:UselessSuper.equivalent_params_2:Useless super delegation in method 'equivalent_params_2'
+useless-super-delegation:120:UselessSuper.equivalent_params_3:Useless super delegation in method 'equivalent_params_3'
+useless-super-delegation:123:UselessSuper.equivalent_params_4:Useless super delegation in method 'equivalent_params_4'
+useless-super-delegation:126:UselessSuper.equivalent_params_5:Useless super delegation in method 'equivalent_params_5'
+useless-super-delegation:129:UselessSuper.equivalent_params_6:Useless super delegation in method 'equivalent_params_6'
+useless-super-delegation:132:UselessSuper.with_default_argument:Useless super delegation in method 'with_default_argument'
+useless-super-delegation:136:UselessSuper.without_default_argument:Useless super delegation in method 'without_default_argument'
+useless-super-delegation:139:UselessSuper.__init__:Useless super delegation in method '__init__'