Looking at the UNARY_NOT case in ceval.c:
case UNARY_NOT:
v = TOP();
err = PyObject_IsTrue(v);
Py_DECREF(v);
if (err == 0) {
Py_INCREF(Py_True);
SET_TOP(Py_True);
continue;
}
else if (err > 0) {
Py_INCREF(Py_False);
SET_TOP(Py_False);
err = 0;
continue;
}
STACKADJ(-1);
break;
I don't understand why there's a STACKADJ(-1) at its end. Looking at the
code, we know that if the CPU arrives to the STACKADJ, it's because of an
error condition in the PyObject_IsTrue that sets err to a < 0 value, so
exiting the big switch statement, an error will be raised.
So the question is, why there's the need to skip the top stack PyObject?
It's a different behaviour comparing it to the all other unary operators.
For example:
case UNARY_NEGATIVE:
v = TOP();
x = PyNumber_Negative(v);
Py_DECREF(v);
SET_TOP(x);
if (x != NULL) continue;
break;
There's no STACKADJ instruction on errors.
Can someone explain it?
Thanks a lot
Cesare
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