8000 gh-111545: Add PyHash_Double() function · python/cpython@ae3843d · GitHub
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gh-111545: Add PyHash_Double() function
* Add again the private _PyHASH_NAN constant. * Add tests: Modules/_testcapi/hash.c and Lib/test/test_capi/test_hash.py.
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‎Doc/c-api/hash.rst

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@@ -5,12 +5,16 @@ PyHash API
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See also the :c:member:`PyTypeObject.tp_hash` member.
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Types
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^^^^^
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.. c:type:: Py_hash_t
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Hash value type: signed integer.
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.. versionadded:: 3.2
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.. c:type:: Py_uhash_t
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Hash value type: unsigned integer.
@@ -41,8 +45,33 @@ See also the :c:member:`PyTypeObject.tp_hash` member.
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.. versionadded:: 3.4
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Functions
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^^^^^^^^^
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.. c:function:: int PyHash_Double(double value, Py_hash_t *result)
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Hash a C double number.
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* Set *\*result* to the hash and return ``1`` if *value* is finite or is
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infinity.
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* Set *\*result* to :data:`sys.hash_info.nan <sys.hash_info>` (``0``) and
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return ``0`` if *value* is not-a-number (NaN).
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*result* must not be ``NULL``.
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.. note::
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Only rely on the function return value to distinguish the "not-a-number"
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case. *\*result* can be ``0`` if *value* is finite. For example,
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``PyHash_Double(0.0, &result)`` sets *\*result* to 0.
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.. versionadded:: 3.13
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.. c:function:: PyHash_FuncDef* PyHash_GetFuncDef(void)
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Get the hash function definition.
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.. seealso::
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:pep:`456` "Secure and interchangeable hash algorithm".
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.. versionadded:: 3.4

‎Doc/library/sys.rst

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@@ -1034,7 +1034,13 @@ always available.
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.. attribute:: hash_info.nan
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(This attribute is no longer used)
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The hash value returned for not-a-number (NaN).
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This hash value is only used by the :c:func:`PyHash_Double` C function if
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the argument is not-a-number (NaN).
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.. versionchanged:: 3.10
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This hash value is no longer used to hash numbers in Python.
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.. attribute:: hash_info.imag
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‎Doc/whatsnew/3.13.rst

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@@ -1196,6 +1196,9 @@ New Features
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:exc:`KeyError` if the key missing.
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(Contributed by Stefan Behnel and Victor Stinner in :gh:`111262`.)
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* Add :c:func:`PyHash_Double` function to hash a C double number.
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(Contributed by Victor Stinner in :gh:`111545`.)
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Porting to Python 3.13
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----------------------

‎Include/cpython/pyhash.h

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@@ -17,6 +17,7 @@
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#define _PyHASH_MODULUS (((size_t)1 << _PyHASH_BITS) - 1)
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#define _PyHASH_INF 314159
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#define _PyHASH_NAN 0
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#define _PyHASH_IMAG _PyHASH_MULTIPLIER
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/* Helpers for hash functions */
@@ -33,3 +34,5 @@ typedef struct {
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} PyHash_FuncDef;
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PyAPI_FUNC(PyHash_FuncDef*) PyHash_GetFuncDef(void);
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PyAPI_FUNC(int) PyHash_Double(double value, Py_hash_t *result);

‎Lib/test/test_capi/test_hash.py

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@@ -1,3 +1,4 @@
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import math
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import sys
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import unittest
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from test.support import import_helper
@@ -31,3 +32,46 @@ def test_hash_getfuncdef(self):
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self.assertEqual(func_def.name, hash_info.algorithm)
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self.assertEqual(func_def.hash_bits, hash_info.hash_bits)
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self.assertEqual(func_def.seed_bits, hash_info.seed_bits)
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def test_hash_double(self):
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# Test PyHash_Double()
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hash_double = _testcapi.hash_double
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def check_number(value, expected):
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self.assertEqual(hash_double(value), (1, expected))
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# test some integers
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integers = [
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*range(1, 30),
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2**30 - 1,
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2 ** 233,
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int(sys.float_info.max),
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]
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for x in integers:
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with self.subTest(x=x):
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check_number(float(x), hash(x))
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check_number(float(-x), hash(-x))
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# test positive and negative zeros
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check_number(float(0.0), 0)
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check_number(float(-0.0), 0)
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# test +inf and -inf
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inf = float("inf")
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check_number(inf, sys.hash_info.inf)
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check_number(-inf, -sys.hash_info.inf)
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# special float values: compare with Python hash() function
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special_values = (
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math.nextafter(0.0, 1.0), # smallest positive subnormal number
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sys.float_info.min, # smallest positive normal number
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sys.float_info.epsilon,
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sys.float_info.max, # largest positive finite number
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)
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for x in special_values:
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with self.subTest(x=x):
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check_number(x, hash(x))
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check_number(-x, hash(-x))
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# test not-a-number (NaN)
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self.assertEqual(hash_double(float('nan')), (0, sys.hash_info.nan))

‎Misc/NEWS.d/next/C API/2023-11-15-01-26-59.gh-issue-111545.iAoFtA.rst

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Add :c:func:`PyHash_Double` function to hash a C double number. Patch by
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Victor Stinner.

‎Modules/_testcapi/hash.c

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#include "parts.h"
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#include "util.h"
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static PyObject *
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hash_getfuncdef(PyObject *Py_UNUSED(module), PyObject *Py_UNUSED(args))
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{
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return result;
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}
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static PyObject *
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hash_double(PyObject *Py_UNUSED(module), PyObject *args)
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{
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double value;
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if (!PyArg_ParseTuple(args, "d", &value)) {
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return NULL;
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}
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Py_hash_t hash;
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int res = PyHash_Double(value, &hash);
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assert(hash != -1);
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Py_BUILD_ASSERT(sizeof(long long) >= sizeof(hash));
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return Py_BuildValue("iN", res, PyLong_FromLongLong(hash));
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}
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static PyMethodDef test_methods[] = {
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{"hash_getfuncdef", hash_getfuncdef, METH_NOARGS},
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{"hash_double", hash_double, METH_VARARGS},
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{NULL},
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};
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‎Python/pyhash.c

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@@ -85,18 +85,23 @@ static Py_ssize_t hashstats[Py_HASH_STATS_MAX + 1] = {0};
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Py_hash_t _Py_HashPointer(const void *);
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Py_hash_t
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_Py_HashDouble(PyObject *inst, double v)
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int
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PyHash_Double(double v, Py_hash_t *result)
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{
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int e, sign;
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double m;
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Py_uhash_t x, y;
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if (!Py_IS_FINITE(v)) {
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if (Py_IS_INFINITY(v))
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return v > 0 ? _PyHASH_INF : -_PyHASH_INF;
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else
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return _Py_HashPointer(inst);
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if (Py_IS_INFINITY(v)) {
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*result = (v > 0 ? _PyHASH_INF : -_PyHASH_INF);
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return 1;
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}
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else {
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assert(Py_IS_NAN(v));
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*result = _PyHASH_NAN;
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return 0;
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}
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}
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m = frexp(v, &e);
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x = x * sign;
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if (x == (Py_uhash_t)-1)
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x = (Py_uhash_t)-2;
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return (Py_hash_t)x;
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*result = (Py_hash_t)x;
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return 1;
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}
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Py_hash_t
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_Py_HashDouble(PyObject *obj, double v)
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{
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assert(obj != NULL);
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Py_hash_t hash;
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if (PyHash_Double(v, &hash) == 0) {
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hash = _Py_HashPointer(obj);
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}
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return hash;
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}
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Py_hash_t

‎Python/sysmodule.c

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@@ -1497,7 +1497,7 @@ get_hash_info(PyThreadState *tstate)
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PyStructSequence_SET_ITEM(hash_info, field++,
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PyLong_FromLong(_PyHASH_INF));
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PyStructSequence_SET_ITEM(hash_info, field++,
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PyLong_FromLong(0)); // This is no longer used
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PyLong_FromLong(_PyHASH_NAN));
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PyStructSequence_SET_ITEM(hash_info, field++,
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PyLong_FromLong(_PyHASH_IMAG));
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PyStructSequence_SET_ITEM(hash_info, field++,

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