Implement new check, N819: TypedDict variable naming

Author: Daniel Patrick

README.rst

@@ -73,6 +73,9 @@ These error codes are emitted:
 +---------+-----------------------------------------------------------------+
 | _`N818` | error suffix in exception names (`exceptions`_)                 |
 +---------+-----------------------------------------------------------------+
+| _`N819` | mixedCase variable in TypedDict subclass                        |
+|         | (distinct from `N815`_ for selective enforcement)               |
++---------+-----------------------------------------------------------------+
 
 .. _class names: https://www.python.org/dev/peps/pep-0008/#class-names
 .. _constants: https://www.python.org/dev/peps/pep-0008/#constants
@@ -88,7 +91,7 @@ The following flake8 options are added:
 
 --ignore-names              Ignore errors for specific names or glob patterns.
 
-                            Currently, this option can only be used for N802, N803, N804, N805, N806, N815, and N816 errors.
+                            Currently, this option can only be used for N802, N803, N804, N805, N806, N815, N816 and N819 errors.
 
                             Default: ``setUp,tearDown,setUpClass,tearDownClass,asyncSetUp,asyncTearDown,setUpTestData,failureException,longMessage,maxDiff``.
 

src/pep8ext_naming.py

@@ -169,7 +169,7 @@ def add_options(cls, parser):
                          help='List of method decorators pep8-naming plugin '
                               'should consider staticmethods (Defaults to '
                               '%default)')
-        parser.extend_default_ignore(['N818'])
+        parser.extend_default_ignore(['N818', 'N819'])
 
     @classmethod
     def parse_options(cls, options):
@@ -449,13 +449,15 @@ class VariablesCheck(BaseASTCheck):
     N806 = "variable '{name}' in function should be lowercase"
     N815 = "variable '{name}' in class scope should not be mixedCase"
     N816 = "variable '{name}' in global scope should not be mixedCase"
+    N819 = "variable '{name}' in TypedDict should not be mixedCase"
 
     def _find_errors(self, assignment_target, parents, ignore):
         for parent_func in reversed(parents):
             if isinstance(parent_func, ast.ClassDef):
                 if "TypedDict" in parent_func.superclasses:
-                    return
-                checker = self.class_variable_check
+                    checker = self.typeddict_variable_check
+                else:
+                    checker = self.class_variable_check
                 break
             if isinstance(parent_func, FUNC_NODES):
                 checker = partial(self.function_variable_check, parent_func)
@@ -544,6 +546,11 @@ def function_variable_check(func, var_name):
             return None
         return 'N806'
 
+    @staticmethod
+    def typeddict_variable_check(name):
+        if is_mixed_case(name):
+            return 'N819'
+
 
 def _extract_names(assignment_target):
     """Yield assignment_target ids."""

testsuite/N815.py

@@ -25,3 +25,9 @@ class C:
 #: Okay(--ignore-names=*Case)
 class C:
     mixed_Case = 0
+#: N815
+class TypedDict:
+    mixedCase: str
+#: N815
+class TypedDict:
+    more_Mixed_Case: str

testsuite/N815_py38.py

@@ -0,0 +1,17 @@
+#: Okay
+class MyDict(TypedDict):
+    snake_case: str
+#: N819
+class MyDict(TypedDict):
+    mixedCase: str
+#: N819
+class MyDict(TypedDict):
+    snake_case: str
+class MyOtherDict(MyDict):
+    more_Mixed_Case: str
+#: Okay(--ignore-names=mixedCase)
+class MyDict(TypedDict):
+    mixedCase: str
+#: Okay(--ignore-names=*Case)
+class MyDict(TypedDict):
+    mixedCase: str