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methanemethane
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benchmark for _PyDict_NewPresized
See python/cpython#139773
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‎2025/dictnew/README.md‎

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Python 3.5
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| Benchmark | dict_new | dict_presized |
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|----------------|:--------:|:---------------------:|
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| dict-1 | 454 ns | 398 ns: 1.14x faster |
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| dict-5 | 2.07 us | 1.73 us: 1.20x faster |
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| dict-10 | 3.96 us | 3.28 us: 1.21x faster |
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| dict-25 | 9.25 us | 7.56 us: 1.22x faster |
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| dict-100 | 31.4 us | 25.6 us: 1.22x faster |
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| dict-500 | 113 us | 103 us: 1.11x faster |
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| dict-1,000 | 218 us | 200 us: 1.09x faster |
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| Geometric mean | (ref) | 1.17x faster |
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Python 3.12
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| Benchmark | dict_new | dict_presized |
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|----------------|:--------:|:---------------------:|
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| dict-1 | 378 ns | 337 ns: 1.12x faster |
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| dict-5 | 1.49 us | 1.34 us: 1.11x faster |
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| dict-10 | 2.65 us | 2.32 us: 1.14x faster |
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| dict-25 | 5.84 us | 5.12 us: 1.14x faster |
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| dict-100 | 22.0 us | 18.0 us: 1.22x faster |
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| dict-500 | 98.6 us | 87.6 us: 1.13x faster |
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| dict-1,000 | 194 us | 172 us: 1.13x faster |
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| Geometric mean | (ref) | 1.14x faster |
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‎2025/dictnew/bench_new.py‎

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import pyperf
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import dictbench
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runner = pyperf.Runner()
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for size in (1, 5, 10, 25, 100, 500, 1000):
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runner.bench_time_func('dict-{:,}'.format(size), dictbench.bench_new, size)

‎2025/dictnew/bench_presized.py‎

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import pyperf
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import dictbench
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runner = pyperf.Runner()
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for size in (1, 5, 10, 25, 100, 500, 1000):
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runner.bench_time_func('dict-{:,}'.format(size), dictbench.bench_presized, size)

‎2025/dictnew/dict_new.json‎

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‎2025/dictnew/dict_new_312.json‎

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‎2025/dictnew/dict_presized.json‎

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‎2025/dictnew/dict_presized_312.json‎

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‎2025/dictnew/dictbench.c‎

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#define PY_SSIZE_T_CLEAN
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#include <Python.h>
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#include <time.h>
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static PyObject *bench_dict_new(PyObject *ob, PyObject *args) {
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Py_ssize_t size, loops;
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if (!PyArg_ParseTuple(args, "nn", &size, &loops)) {
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return NULL;
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}
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struct timespec start, end;
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clock_gettime(CLOCK_MONOTONIC, &start);
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for (Py_ssize_t loop = 0; loop < loops; loop++) {
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PyObject *d = PyDict_New();
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if (d == NULL) {
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return NULL;
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}
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for (Py_ssize_t i = 0; i < size; i++) {
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PyObject *key = PyUnicode_FromFormat("%zi", i);
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assert(key != NULL);
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PyObject *value = PyLong_FromLong(i);
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assert(value != NULL);
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PyDict_SetItem(d, key, value);
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Py_DECREF(key);
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Py_DECREF(value);
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}
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assert(PyDict_Size(d) == size);
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Py_DECREF(d);
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}
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clock_gettime(CLOCK_MONOTONIC, &end);
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double time_spent = (end.tv_sec - start.tv_sec) +
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(end.tv_nsec - start.tv_nsec) / 1000000000.0;
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return PyFloat_FromDouble(time_spent);
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}
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static PyObject *bench_dict_presized(PyObject *ob, PyObject *args) {
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Py_ssize_t size, loops;
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if (!PyArg_ParseTuple(args, "nn", &size, &loops)) {
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return NULL;
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}
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struct timespec start, end;
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clock_gettime(CLOCK_MONOTONIC, &start);
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for (Py_ssize_t loop = 0; loop < loops; loop++) {
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PyObject *d = _PyDict_NewPresized(size);
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if (d == NULL) {
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return NULL;
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}
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for (Py_ssize_t i = 0; i < size; i++) {
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PyObject *key = PyUnicode_FromFormat("%zi", i);
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assert(key != NULL);
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PyObject *value = PyLong_FromLong(i);
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assert(value != NULL);
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PyDict_SetItem(d, key, value);
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Py_DECREF(key);
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Py_DECREF(value);
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}
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assert(PyDict_Size(d) == size);
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Py_DECREF(d);
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}
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clock_gettime(CLOCK_MONOTONIC, &end);
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double time_spent = (end.tv_sec - start.tv_sec) +
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(end.tv_nsec - start.tv_nsec) / 1000000000.0;
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return PyFloat_FromDouble(time_spent);
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}
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static PyMethodDef DictBenchMethods[] = {
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{"bench_new", bench_dict_new, METH_VARARGS, "Benchmark PyDict_New."},
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{"bench_presized", bench_dict_presized, METH_VARARGS,
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"Benchmark _PyDict_NewPresized."},
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{NULL, NULL, 0, NULL} /* Sentinel */
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};
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static struct PyModuleDef dictbenchmodule = {
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PyModuleDef_HEAD_INIT, "dictbench", /* name of module */
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NULL, /* module documentation, may be NULL */
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-1, /* size of per-interpreter state of the module,
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or -1 if the module keeps state in global variables. */
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DictBenchMethods};
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PyMODINIT_FUNC PyInit_dictbench(void) {
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return PyModule_Create(&dictbenchmodule);
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}

‎2025/dictnew/setup.py‎

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from setuptools import setup, Extension
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module1 = Extension('dictbench',
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sources = ['dictbench.c'])
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setup (name = 'DictBench',
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version = '1.0',
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description = 'Microbenchmark for dict creation',
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ext_modules = [module1])

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