Add B043: Do not call delattr with constant (#514)

Author: fennr

README.rst

@@ -286,10 +286,20 @@ second usage. Save the result to a list if the result is needed multiple times.
 
 **B040**: Caught exception with call to ``add_note`` not used. Did you forget to ``raise`` it?
 
+.. _B041:
+
 **B041**: Repeated key-value pair in dictionary literal. Only emits errors when the key's value is *also* the same, being the opposite of the pyflakes like check.
 
+.. _B042:
+
 **B042**: Remember to call super().__init__() in custom exceptions initalizer.
 
+.. _B043:
+
+**B043**: Do not call ``delattr(x, 'attr')``, instead use ``del x.attr``. 
+There is no additional safety in using ``delattr`` if you know the attribute name ahead of time.
+
+
 Opinionated warnings
 ~~~~~~~~~~~~~~~~~~~~
 

bugbear.py

@@ -523,6 +523,13 @@ def visit_Call(self, node) -> None:
                     and not iskeyword(node.args[1].value)
                 ):
                     self.add_error("B010", node)
+                elif (
+                    node.func.id == "delattr"
+                    and len(node.args) == 2
+                    and _is_identifier(node.args[1])
+                    and not iskeyword(node.args[1].value)
+                ):
+                    self.add_error("B043", node)
 
         self.check_for_b026(node)
         self.check_for_b028(node)
@@ -2415,6 +2422,12 @@ def __call__(self, lineno: int, col: int, vars: tuple[object, ...] = ()) -> erro
             "It should also not take any kwargs."
         )
     ),
+    "B043": Error(
+        message=(
+            "B043 Do not call delattr with a constant attribute value, "
+            "it is not any safer than normal property access."
+        )
+    ),
     # Warnings disabled by default.
     "B901": Error(
         message=(

tests/eval_files/b043.py

@@ -0,0 +1,11 @@
+# Valid usage
+attr_name = "name"
+delattr(obj, attr_name)
+for field in fields_to_remove:
+    delattr(obj, field)
+delattr(obj, some_name())
+delattr(obj, f"field_{index}")
+
+# Invalid usage
+delattr(obj, "name")  # B043: 0
+delattr(obj, r"raw_attr")  # B043: 0