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build_class(): one more (hopefully the last) step on the way to 

backwards compatibility.  When using the class of the first base as
the metaclass, use its __class__ attribute in preference over its
ob_type slot.  This ensures that we can still use classic classes as
metaclasse, as shown in the original "Metaclasses" essay.  This also
makes all the examples in Demo/metaclasses/ work again (maybe these
should be turned into a test suite?).
This commit is contained in:
Guido van Rossum 2001-09-12 19:19:18 +00:00
parent 2400fa4ad1
commit 7851eea5f2
1 changed files with 21 additions and 14 deletions
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25
Python/ceval.c
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@ -3500,25 +3500,32 @@ import_all_from(PyObject *locals, PyObject *v)
static PyObject *
build_class(PyObject *methods, PyObject *bases, PyObject *name)
{
PyObject *metaclass = NULL;
PyObject *metaclass = NULL, *result, *base;
if (PyDict_Check(methods))
metaclass = PyDict_GetItemString(methods, "__metaclass__");
if (metaclass != NULL)
Py_INCREF(methods);
else if (PyTuple_Check(bases) && PyTuple_GET_SIZE(bases) > 0) {
base = PyTuple_GET_ITEM(bases, 0);
metaclass = PyObject_GetAttrString(base, "__class__");
if (metaclass == NULL) {
if (PyTuple_Check(bases) && PyTuple_GET_SIZE(bases) > 0)
metaclass = (PyObject *)
PyTuple_GET_ITEM(bases, 0)->ob_type;
PyErr_Clear();
metaclass = (PyObject *)base->ob_type;
Py_INCREF(metaclass);
}
}
else {
PyObject *g = PyEval_GetGlobals();
if (g != NULL && PyDict_Check(g))
metaclass = PyDict_GetItemString(
g, "__metaclass__");
metaclass = PyDict_GetItemString(g, "__metaclass__");
if (metaclass == NULL)
metaclass = (PyObject *) &PyClass_Type;
Py_INCREF(metaclass);
}
}
return PyObject_CallFunction(metaclass, "OOO", name, bases, methods);
result = PyObject_CallFunction(metaclass, "OOO", name, bases, methods);
Py_DECREF(metaclass);
return result;
}
static int