Add bad-dunder-name checker

doc/data/messages/b/bad-dunder-name/bad.py

@@ -0,0 +1,6 @@
+class Apples:
+    def _init_(self):  # [bad-dunder-name]
+        pass
+
+    def __hello__(self):  # [bad-dunder-name]
+        print("hello")

doc/data/messages/b/bad-dunder-name/good.py

@@ -0,0 +1,6 @@
+class Apples:
+    def __init__(self):
+        pass
+
+    def hello(self):
+        print("hello")

doc/data/messages/b/bad-dunder-name/pylintrc

@@ -0,0 +1,2 @@
+[MAIN]
+load-plugins=pylint.extensions.dunder

doc/whatsnew/fragments/3038.new_check

@@ -0,0 +1,4 @@
+Added ``bad-dunder-name`` extension check, which flags bad or misspelled dunder methods.
+You can use the ``good-dunder-names`` option to allow specific dunder names.
+
+Closes #3038

pylint/checkers/dunder_methods.py

@@ -10,122 +10,19 @@
 
 from pylint.checkers import BaseChecker
 from pylint.checkers.utils import safe_infer
+from pylint.constants import DUNDER_METHODS
 from pylint.interfaces import HIGH
 
 if TYPE_CHECKING:
     from pylint.lint import PyLinter
 
 
-DUNDER_METHODS: dict[tuple[int, int], dict[str, str]] = {
-    (0, 0): {
-        "__init__": "Instantiate class directly",
-        "__del__": "Use del keyword",
-        "__repr__": "Use repr built-in function",
-        "__str__": "Use str built-in function",
-        "__bytes__": "Use bytes built-in function",
-        "__format__": "Use format built-in function, format string method, or f-string",
-        "__lt__": "Use < operator",
-        "__le__": "Use <= operator",
-        "__eq__": "Use == operator",
-        "__ne__": "Use != operator",
-        "__gt__": "Use > operator",
-        "__ge__": "Use >= operator",
-        "__hash__": "Use hash built-in function",
-        "__bool__": "Use bool built-in function",
-        "__getattr__": "Access attribute directly or use getattr built-in function",
-        "__getattribute__": "Access attribute directly or use getattr built-in function",
-        "__setattr__": "Set attribute directly or use setattr built-in function",
-        "__delattr__": "Use del keyword",
-        "__dir__": "Use dir built-in function",
-        "__get__": "Use get method",
-        "__set__": "Use set method",
-        "__delete__": "Use del keyword",
-        "__instancecheck__": "Use isinstance built-in function",
-        "__subclasscheck__": "Use issubclass built-in function",
-        "__call__": "Invoke instance directly",
-        "__len__": "Use len built-in function",
-        "__length_hint__": "Use length_hint method",
-        "__getitem__": "Access item via subscript",
-        "__setitem__": "Set item via subscript",
-        "__delitem__": "Use del keyword",
-        "__iter__": "Use iter built-in function",
-        "__next__": "Use next built-in function",
-        "__reversed__": "Use reversed built-in function",
-        "__contains__": "Use in keyword",
-        "__add__": "Use + operator",
-        "__sub__": "Use - operator",
-        "__mul__": "Use * operator",
-        "__matmul__": "Use @ operator",
-        "__truediv__": "Use / operator",
-        "__floordiv__": "Use // operator",
-        "__mod__": "Use % operator",
-        "__divmod__": "Use divmod built-in function",
-        "__pow__": "Use ** operator or pow built-in function",
-        "__lshift__": "Use << operator",
-        "__rshift__": "Use >> operator",
-        "__and__": "Use & operator",
-        "__xor__": "Use ^ operator",
-        "__or__": "Use | operator",
-        "__radd__": "Use + operator",
-        "__rsub__": "Use - operator",
-        "__rmul__": "Use * operator",
-        "__rmatmul__": "Use @ operator",
-        "__rtruediv__": "Use / operator",
-        "__rfloordiv__": "Use // operator",
-        "__rmod__": "Use % operator",
-        "__rdivmod__": "Use divmod built-in function",
-        "__rpow__": "Use ** operator or pow built-in function",
-        "__rlshift__": "Use << operator",
-        "__rrshift__": "Use >> operator",
-        "__rand__": "Use & operator",
-        "__rxor__": "Use ^ operator",
-        "__ror__": "Use | operator",
-        "__iadd__": "Use += operator",
-        "__isub__": "Use -= operator",
-        "__imul__": "Use *= operator",
-        "__imatmul__": "Use @= operator",
-        "__itruediv__": "Use /= operator",
-        "__ifloordiv__": "Use //= operator",
-        "__imod__": "Use %= operator",
-        "__ipow__": "Use **= operator",
-        "__ilshift__": "Use <<= operator",
-        "__irshift__": "Use >>= operator",
-        "__iand__": "Use &= operator",
-        "__ixor__": "Use ^= operator",
-        "__ior__": "Use |= operator",
-        "__neg__": "Multiply by -1 instead",
-        "__pos__": "Multiply by +1 instead",
-        "__abs__": "Use abs built-in function",
-        "__invert__": "Use ~ operator",
-        "__complex__": "Use complex built-in function",
-        "__int__": "Use int built-in function",
-        "__float__": "Use float built-in function",
-        "__round__": "Use round built-in function",
-        "__trunc__": "Use math.trunc function",
-        "__floor__": "Use math.floor function",
-        "__ceil__": "Use math.ceil function",
-        "__enter__": "Invoke context manager directly",
-        "__aenter__": "Invoke context manager directly",
-        "__copy__": "Use copy.copy function",
-        "__deepcopy__": "Use copy.deepcopy function",
-        "__fspath__": "Use os.fspath function instead",
-    },
-    (3, 10): {
-        "__aiter__": "Use aiter built-in function",
-        "__anext__": "Use anext built-in function",
-    },
-}
-
-
 class DunderCallChecker(BaseChecker):
     """Check for unnecessary dunder method calls.
 
     Docs: https://docs.python.org/3/reference/datamodel.html#basic-customization
-    We exclude __new__, __subclasses__, __init_subclass__, __set_name__,
-    __class_getitem__, __missing__, __exit__, __await__,
-    __aexit__, __getnewargs_ex__, __getnewargs__, __getstate__,
-    __setstate__, __reduce__, __reduce_ex__,
-    and __index__ (see https://github.com/PyCQA/pylint/issues/6795)
+    We exclude names in list pylint.constants.EXTRA_DUNDER_METHODS such as
+    __index__ (see https://github.com/PyCQA/pylint/issues/6795)
     since these either have no alternative method of being called or
     have a genuine use case for being called manually.
 

pylint/constants.py

@@ -168,3 +168,133 @@ def _get_pylint_home() -> str:
         "typing_extensions.Never",
     )
 )
+
+DUNDER_METHODS: dict[tuple[int, int], dict[str, str]] = {
+    (0, 0): {
+        "__init__": "Instantiate class directly",
+        "__del__": "Use del keyword",
+        "__repr__": "Use repr built-in function",
+        "__str__": "Use str built-in function",
+        "__bytes__": "Use bytes built-in function",
+        "__format__": "Use format built-in function, format string method, or f-string",
+        "__lt__": "Use < operator",
+        "__le__": "Use <= operator",
+        "__eq__": "Use == operator",
+        "__ne__": "Use != operator",
+        "__gt__": "Use > operator",
+        "__ge__": "Use >= operator",
+        "__hash__": "Use hash built-in function",
+        "__bool__": "Use bool built-in function",
+        "__getattr__": "Access attribute directly or use getattr built-in function",
+        "__getattribute__": "Access attribute directly or use getattr built-in function",
+        "__setattr__": "Set attribute directly or use setattr built-in function",
+        "__delattr__": "Use del keyword",
+        "__dir__": "Use dir built-in function",
+        "__get__": "Use get method",
+        "__set__": "Use set method",
+        "__delete__": "Use del keyword",
+        "__instancecheck__": "Use isinstance built-in function",
+        "__subclasscheck__": "Use issubclass built-in function",
+        "__call__": "Invoke instance directly",
+        "__len__": "Use len built-in function",
+        "__length_hint__": "Use length_hint method",
+        "__getitem__": "Access item via subscript",
+        "__setitem__": "Set item via subscript",
+        "__delitem__": "Use del keyword",
+        "__iter__": "Use iter built-in function",
+        "__next__": "Use next built-in function",
+        "__reversed__": "Use reversed built-in function",
+        "__contains__": "Use in keyword",
+        "__add__": "Use + operator",
+        "__sub__": "Use - operator",
+        "__mul__": "Use * operator",
+        "__matmul__": "Use @ operator",
+        "__truediv__": "Use / operator",
+        "__floordiv__": "Use // operator",
+        "__mod__": "Use % operator",
+        "__divmod__": "Use divmod built-in function",
+        "__pow__": "Use ** operator or pow built-in function",
+        "__lshift__": "Use << operator",
+        "__rshift__": "Use >> operator",
+        "__and__": "Use & operator",
+        "__xor__": "Use ^ operator",
+        "__or__": "Use | operator",
+        "__radd__": "Use + operator",
+        "__rsub__": "Use - operator",
+        "__rmul__": "Use * operator",
+        "__rmatmul__": "Use @ operator",
+        "__rtruediv__": "Use / operator",
+        "__rfloordiv__": "Use // operator",
+        "__rmod__": "Use % operator",
+        "__rdivmod__": "Use divmod built-in function",
+        "__rpow__": "Use ** operator or pow built-in function",
+        "__rlshift__": "Use << operator",
+        "__rrshift__": "Use >> operator",
+        "__rand__": "Use & operator",
+        "__rxor__": "Use ^ operator",
+        "__ror__": "Use | operator",
+        "__iadd__": "Use += operator",
+        "__isub__": "Use -= operator",
+        "__imul__": "Use *= operator",
+        "__imatmul__": "Use @= operator",
+        "__itruediv__": "Use /= operator",
+        "__ifloordiv__": "Use //= operator",
+        "__imod__": "Use %= operator",
+        "__ipow__": "Use **= operator",
+        "__ilshift__": "Use <<= operator",
+        "__irshift__": "Use >>= operator",
+        "__iand__": "Use &= operator",
+        "__ixor__": "Use ^= operator",
+        "__ior__": "Use |= operator",
+        "__neg__": "Multiply by -1 instead",
+        "__pos__": "Multiply by +1 instead",
+        "__abs__": "Use abs built-in function",
+        "__invert__": "Use ~ operator",
+        "__complex__": "Use complex built-in function",
+        "__int__": "Use int built-in function",
+        "__float__": "Use float built-in function",
+        "__round__": "Use round built-in function",
+        "__trunc__": "Use math.trunc function",
+        "__floor__": "Use math.floor function",
+        "__ceil__": "Use math.ceil function",
+        "__enter__": "Invoke context manager directly",
+        "__aenter__": "Invoke context manager directly",
+        "__copy__": "Use copy.copy function",
+        "__deepcopy__": "Use copy.deepcopy function",
+        "__fspath__": "Use os.fspath function instead",
+    },
+    (3, 10): {
+        "__aiter__": "Use aiter built-in function",
+        "__anext__": "Use anext built-in function",
+    },
+}
+
+EXTRA_DUNDER_METHODS = [
+    "__new__",
+    "__subclasses__",
+    "__init_subclass__",
+    "__set_name__",
+    "__class_getitem__",
+    "__missing__",
+    "__exit__",
+    "__await__",
+    "__aexit__",
+    "__getnewargs_ex__",
+    "__getnewargs__",
+    "__getstate__",
+    "__setstate__",
+    "__reduce__",
+    "__reduce_ex__",
+    "__post_init__",  # part of `dataclasses` module
+]
+
+DUNDER_PROPERTIES = [
+    "__class__",
+    "__dict__",
+    "__doc__",
+    "__format__",
+    "__module__",
+    "__sizeof__",
+    "__subclasshook__",
+    "__weakref__",
+]

pylint/extensions/dunder.py

@@ -0,0 +1,77 @@
+# Licensed under the GPL: https://www.gnu.org/licenses/old-licenses/gpl-2.0.html
+# For details: https://github.com/PyCQA/pylint/blob/main/LICENSE
+# Copyright (c) https://github.com/PyCQA/pylint/blob/main/CONTRIBUTORS.txt
+
+from __future__ import annotations
+
+from typing import TYPE_CHECKING
+
+from astroid import nodes
+
+from pylint.checkers import BaseChecker
+from pylint.constants import DUNDER_METHODS, DUNDER_PROPERTIES, EXTRA_DUNDER_METHODS
+from pylint.interfaces import HIGH
+
+if TYPE_CHECKING:
+    from pylint.lint import PyLinter
+
+
+class DunderChecker(BaseChecker):
+    """Checks related to dunder methods."""
+
+    name = "dunder"
+    priority = -1
+    msgs = {
+        "W3201": (
+            "Bad or misspelled dunder method name %s.",
+            "bad-dunder-name",
+            "Used when a dunder method is misspelled or defined with a name "
+            "not within the predefined list of dunder names.",
+        ),
+    }
+    options = (
+        (
+            "good-dunder-names",
+            {
+                "default": [],
+                "type": "csv",
+                "metavar": "<comma-separated names>",
+                "help": "Good dunder names which should always be accepted.",
+            },
+        ),
+    )
+
+    def open(self) -> None:
+        self._dunder_methods = (
+            EXTRA_DUNDER_METHODS
+            + DUNDER_PROPERTIES
+            + self.linter.config.good_dunder_names
+        )
+        for since_vers, dunder_methods in DUNDER_METHODS.items():
+            if since_vers <= self.linter.config.py_version:
+                self._dunder_methods.extend(list(dunder_methods.keys()))
+
+    def visit_functiondef(self, node: nodes.FunctionDef) -> None:
+        """Check if known dunder method is misspelled or dunder name is not one
+        of the pre-defined names.
+        """
+        # ignore module-level functions
+        if not node.is_method():
+            return
+
+        # Detect something that could be a bad dunder method
+        if (
+            node.name.startswith("_")
+            and node.name.endswith("_")
+            and node.name not in self._dunder_methods
+        ):
+            self.add_message(
+                "bad-dunder-name",
+                node=node,
+                args=(node.name),
+                confidence=HIGH,
+            )
+
+
+def register(linter: PyLinter) -> None:
+    linter.register_checker(DunderChecker(linter))