check for class methods declared without a decorator

related to the issue #675

1 files changed, 36 insertions, 3 deletions

diff --git a/pylint/checkers/classes.py b/pylint/checkers/classes.py
index 86ccb19..98a13bf 100644
--- a/pylint/checkers/classes.py
+++ b/pylint/checkers/classes.py
@@ -262,7 +262,10 @@ MSGS = {
     'E0241': ('Duplicate bases for class %r',
               'duplicate-bases',
               'Used when a class has duplicate bases.'),
-
+    'R0202': ('Consider using a decorator instead of calling classmethod',
+              'no-classmethod-decorator',
+              'Used when a class method is defined without using the decorator '
+              'syntax.'),
     }
 
 
@@ -613,17 +616,47 @@ a metaclass class method.'}
                     self.add_message('assigning-non-slot',
                                      args=(node.attrname, ), node=node)
 
-    @check_messages('protected-access')
+    @check_messages('protected-access', 'no-classmethod-decorator')
     def visit_assign(self, assign_node):
+        self._check_classmethod_declaration(assign_node)
         node = assign_node.targets[0]
         if not isinstance(node, astroid.AssignAttr):
             return
 
         if self.is_first_attr(node):
             return
-
         self._check_protected_attribute_access(node)
 
+    def _check_classmethod_declaration(self, node):
+        """checks for uses of classmethod() instead of @classmethod decorator
+
+        A message will be emitted only if the assignment is at a class scope
+        and only if the classmethod's argument belongs to the class where it
+        is defined.
+        `node` is an assign node.
+        """
+        if not isinstance(node.value, astroid.Call):
+            return
+        # check the function called is "classmethod"
+        func = node.value.func
+        if not isinstance(func, astroid.Name) or not func.name == 'classmethod':
+            return
+        # assignment must be at a class scope
+        parent_class = node.parent
+        if not isinstance(parent_class, astroid.ClassDef):
+            return
+        # Check if the arg passed to classmethod is a class member
+        classmeth_arg = node.value.args[0]
+        if not isinstance(classmeth_arg, astroid.Name):
+            return
+        method_name = classmeth_arg.name
+        for member in parent_class.get_children():
+            if (isinstance(member, astroid.FunctionDef) and
+                    method_name == member.name):
+                self.add_message('no-classmethod-decorator',
+                                 node=node.targets[0])
+                break
+
     def _check_protected_attribute_access(self, node):
         '''Given an attribute access node (set or get), check if attribute
         access is legitimate. Call _check_first_attr with node before calling