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gh-138890: Add clearer message when deleting builtins with del #139078

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1de2683
Add clearer message when deleting builtins with del
Tapeline Sep 17, 2025
8bf802d
Fix forgotten argument
Tapeline Sep 17, 2025
9c94cbe
Make some styling changes.
Tapeline Sep 19, 2025
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24 changes: 24 additions & 0 deletions Lib/test/test_scope.py
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Original file line number Diff line number Diff line change
Expand Up @@ -835,5 +835,29 @@ def g(self, __arg):
with self.assertRaises(TypeError):
closure(_MultiplyNested__arg=2)

def test_builtin_deletion_err_message(self):
with self.assertRaisesRegex(
NameError, "cannot delete builtin 'all'"
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The formatting makes this a bit difficult to read. This isn't coming near PEP 8's 79 character limit, so let's just keep all the arguments on the same line. This applies to all the assertRaisesRegex calls below.

):
del all

def f():
del all

with self.assertRaisesRegex(
UnboundLocalError, "cannot delete builtin 'all'"
):
f()

def g():
global all
del all

with self.assertRaisesRegex(
NameError, "cannot delete builtin 'all'"
):
g()


if __name__ == '__main__':
unittest.main()
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core_and_Builtins/2025-09-18-01-13-22.gh-issue-138890.x2QKfy.rst
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@@ -0,0 +1 @@
Deleting builtin names with ``del`` now gives a clearer error message.
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Suggested change
Deleting builtin names with ``del`` now gives a clearer error message.
Deleting built-in names with :keyword:`del` now gives a clearer error message.

23 changes: 15 additions & 8 deletions Python/bytecodes.c
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Expand Up @@ -1577,9 +1577,10 @@ dummy_func(
err = PyObject_DelItem(ns, name);
// Can't use ERROR_IF here.
if (err != 0) {
_PyEval_FormatExcCheckArg(tstate, PyExc_NameError,
NAME_ERROR_MSG,
name);
const char *err_msg = PyMapping_HasKey(BUILTINS(), name)
? CANNOT_DELETE_BUILTIN_ERROR_MSG
: NAME_ERROR_MSG;
_PyEval_FormatExcCheckArg(tstate, PyExc_NameError, err_msg, name);
ERROR_NO_POP();
}
}
Expand Down Expand Up @@ -1720,8 +1721,11 @@ dummy_func(
ERROR_NO_POP();
}
if (err == 0) {
const char *err_msg = PyMapping_HasKey(BUILTINS(), name)
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I believe it is safe to use PyDict_* here.

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There's no PyDict_* equivalent of PyMapping_HasKey, but we should be using PyMapping_HasKeyWithError here.

? CANNOT_DELETE_BUILTIN_ERROR_MSG
: NAME_ERROR_MSG;
_PyEval_FormatExcCheckArg(tstate, PyExc_NameError,
NAME_ERROR_MSG, name);
err_msg, name);
ERROR_NO_POP();
}
}
Expand Down Expand Up @@ -1888,10 +1892,13 @@ dummy_func(
inst(DELETE_FAST, (--)) {
_PyStackRef v = GETLOCAL(oparg);
if (PyStackRef_IsNull(v)) {
_PyEval_FormatExcCheckArg(tstate, PyExc_UnboundLocalError,
UNBOUNDLOCAL_ERROR_MSG,
PyTuple_GetItem(_PyFrame_GetCode(frame)->co_localsplusnames, oparg)
);
PyObject *name;
name = PyTuple_GetItem(_PyFrame_GetCode(frame)->co_localsplusnames,
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PyTuple_GetItem can fail. We should be able to expect that it can't, so let's use PyTuple_GET_ITEM.

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Shouldn't we leave this as is? This seems like an unrelated change.

oparg);
const char *err_msg = PyMapping_HasKey(BUILTINS(), name)
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Ditto -- we should be using PyMapping_HasKeyWithError.

? CANNOT_DELETE_BUILTIN_ERROR_MSG
: UNBOUNDLOCAL_ERROR_MSG;
_PyEval_FormatExcCheckArg(tstate, PyExc_UnboundLocalError, err_msg, name);
ERROR_IF(true);
}
_PyStackRef tmp = GETLOCAL(oparg);
Expand Down
1 change: 1 addition & 0 deletions Python/ceval_macros.h
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Expand Up @@ -303,6 +303,7 @@ GETITEM(PyObject *v, Py_ssize_t i) {
"cannot access free variable '%s' where it is not associated with a value" \
" in enclosing scope"
#define NAME_ERROR_MSG "name '%.200s' is not defined"
#define CANNOT_DELETE_BUILTIN_ERROR_MSG "cannot delete builtin '%.200s'"

// If a trace function sets a new f_lineno and
// *then* raises, we use the destination when searching
Expand Down
23 changes: 15 additions & 8 deletions Python/executor_cases.c.h
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23 changes: 15 additions & 8 deletions Python/generated_cases.c.h
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