mirror of https://github.com/python/cpython
bpo-31506: Improve the error message logic for class instantiation (GH-4740)
The error messages in `object.__new__` and `object.__init__` now aim to point the user more directly at the name of the class being instantiated in cases where they *haven't* been overridden (on the assumption that the actual problem is a missing `__new__` or `__init__` definition in the class body). When they *have* been overridden, the errors still report themselves as coming from object, on the assumption that the problem is with the call up to the base class in the method implementation, rather than with the way the constructor is being called.
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@ -595,5 +595,54 @@ class ClassTests(unittest.TestCase):
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with self.assertRaises(TypeError):
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type.__setattr__(A, b'x', None)
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def testConstructorErrorMessages(self):
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# bpo-31506: Improves the error message logic for object_new & object_init
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# Class without any method overrides
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class C:
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pass
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with self.assertRaisesRegex(TypeError, r'C\(\) takes no arguments'):
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C(42)
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with self.assertRaisesRegex(TypeError, r'C\(\) takes no arguments'):
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C.__new__(C, 42)
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with self.assertRaisesRegex(TypeError, r'C\(\).__init__\(\) takes no arguments'):
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C().__init__(42)
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with self.assertRaisesRegex(TypeError, r'C\(\) takes no arguments'):
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object.__new__(C, 42)
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with self.assertRaisesRegex(TypeError, r'C\(\).__init__\(\) takes no arguments'):
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object.__init__(C(), 42)
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# Class with both `__init__` & `__new__` method overriden
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class D:
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def __new__(cls, *args, **kwargs):
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super().__new__(cls, *args, **kwargs)
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def __init__(self, *args, **kwargs):
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super().__init__(*args, **kwargs)
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with self.assertRaisesRegex(TypeError, r'object.__new__\(\) takes no argument'):
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D(42)
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with self.assertRaisesRegex(TypeError, r'object.__new__\(\) takes no argument'):
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D.__new__(D, 42)
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with self.assertRaisesRegex(TypeError, r'object.__new__\(\) takes no argument'):
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object.__new__(D, 42)
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# Class that only overrides __init__
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class E:
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def __init__(self, *args, **kwargs):
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super().__init__(*args, **kwargs)
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with self.assertRaisesRegex(TypeError, r'object.__init__\(\) takes no argument'):
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E().__init__(42)
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with self.assertRaisesRegex(TypeError, r'object.__init__\(\) takes no argument'):
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object.__init__(E(), 42)
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if __name__ == '__main__':
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unittest.main()
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@ -0,0 +1,2 @@
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Improve the error message logic for object.__new__ and object.__init__.
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Patch by Sanyam Khurana.
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@ -3592,11 +3592,11 @@ object_init(PyObject *self, PyObject *args, PyObject *kwds)
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PyTypeObject *type = Py_TYPE(self);
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if (excess_args(args, kwds)) {
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if (type->tp_init != object_init) {
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PyErr_SetString(PyExc_TypeError, "object() takes no arguments");
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PyErr_SetString(PyExc_TypeError, "object.__init__() takes no arguments");
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return -1;
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}
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if (type->tp_new == object_new) {
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PyErr_Format(PyExc_TypeError, "%.200s() takes no arguments",
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PyErr_Format(PyExc_TypeError, "%.200s().__init__() takes no arguments",
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type->tp_name);
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return -1;
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}
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@ -3609,7 +3609,7 @@ object_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
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{
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if (excess_args(args, kwds)) {
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if (type->tp_new != object_new) {
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PyErr_SetString(PyExc_TypeError, "object() takes no arguments");
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PyErr_SetString(PyExc_TypeError, "object.__new__() takes no arguments");
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return NULL;
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}
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if (type->tp_init == object_init) {
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