[New-bugs-announce] [issue31791] Ensure that all PyTypeObject fields are set to non-NULL defaults
pdox
report at bugs.python.org
Sun Oct 15 02:22:29 EDT 2017
New submission from pdox <pdox at alum.mit.edu>:
Ensure that every function pointer in every PyTypeObject is set to a non-NULL default, to spare the cost of checking for NULL with every use. As a basic example, consider PyNumber_Negative:
PyObject *
PyNumber_Negative(PyObject *o)
{
PyNumberMethods *m;
if (o == NULL) {
return null_error();
}
m = o->ob_type->tp_as_number;
if (m && m->nb_negative)
return (*m->nb_negative)(o);
return type_error("bad operand type for unary -: '%.200s'", o);
}
If "tp_as_number" and "nb_negative" were always guaranteed non-NULL, then the function could omit the second if statement, and invoke the function pointer directly. To maintain the existing behavior, the default nb_negative function would be set to the following:
PyObject* nb_negative_default(PyObject *o) {
return type_error("bad operand type for unary -: '%.200s'", o);
}
This removes two NULL-checks from the PyNumber_Negative. Many other operators and builtins would be able to benefit in the same way.
----------
components: Interpreter Core
messages: 304420
nosy: pdox
priority: normal
severity: normal
status: open
title: Ensure that all PyTypeObject fields are set to non-NULL defaults
type: performance
versions: Python 3.7
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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue31791>
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