PyHash API

See also the PyTypeObject.tp_hash member and Hashing of numeric types.

type Py_hash_t

Hash value type: signed integer.

Added in version 3.2.

type Py_uhash_t

Hash value type: unsigned integer.

Added in version 3.2.

Py_HASH_ALGORITHM

A numerical value indicating the algorithm for hashing of str, bytes, and memoryview.

The algorithm name is exposed by sys.hash_info.algorithm.

Added in version 3.4.

Py_HASH_FNV

Py_HASH_SIPHASH24

Py_HASH_SIPHASH13

Numerical values to compare to Py_HASH_ALGORITHM to determine which algorithm is used for hashing. The hash algorithm can be configured via the configure --with-hash-algorithm option.

Added in version 3.4: Add Py_HASH_FNV and Py_HASH_SIPHASH24.

Added in version 3.13: Add Py_HASH_SIPHASH13.

Py_HASH_CUTOFF

Buffers of length in range [1, Py_HASH_CUTOFF) are hashed using DJBX33A instead of the algorithm described by Py_HASH_ALGORITHM.

• A Py_HASH_CUTOFF of 0 disables the optimization.

• Py_HASH_CUTOFF must be non-negative and less or equal than 7.

32-bit platforms should use a cutoff smaller than 64-bit platforms because it is easier to create colliding strings. A cutoff of 7 on 64-bit platforms and 5 on 32-bit platforms should provide a decent safety margin.

Added in version 3.4.

PyHASH_MODULUS

The Mersenne prime P = 2**n -1, used for numeric hash scheme. This corresponds to the sys.hash_info.modulus constant.

Added in version 3.13.

PyHASH_BITS

The exponent n of P in PyHASH_MODULUS. This corresponds to the sys.hash_info.hash_bits constant.

Added in version 3.13.

PyHASH_MULTIPLIER

Prime multiplier used in string and various other hashes.

Added in version 3.13.

PyHASH_INF

The hash value returned for a positive infinity. This corresponds to the sys.hash_info.inf constant.

Added in version 3.13.

PyHASH_IMAG

The multiplier used for the imaginary part of a complex number. This corresponds to the sys.hash_info.imag constant.

Added in version 3.13.

type PyHash_FuncDef

Hash function definition used by PyHash_GetFuncDef().

Py_hash_t (*const hash)(const void*, Py_ssize_t)

Hash function.

const char *name

Hash function name (UTF-8 encoded string).

const int hash_bits

Internal size of the hash value in bits.

const int seed_bits

Size of seed input in bits.

Added in version 3.4.

PyHash_FuncDef *PyHash_GetFuncDef(void)

Get the hash function definition.

See also

PEP 456 “Secure and interchangeable hash algorithm”.

Added in version 3.4.

Py_hash_t Py_HashPointer(const void *ptr)

Hash a pointer value: process the pointer value as an integer (cast it to uintptr_t internally). The pointer is not dereferenced.

The function cannot fail: it cannot return -1.

Added in version 3.13.

Py_hash_t Py_HashBuffer(const void *ptr, Py_ssize_t len)

Compute and return the hash value of a buffer of len bytes starting at address ptr. The hash is guaranteed to match that of bytes, memoryview, and other built-in objects that implement the buffer protocol.

Use this function to implement hashing for immutable objects whose tp_richcompare function compares to another object’s buffer.

len must be greater than or equal to 0.

This function always succeeds.

Added in version 3.14.

Py_hash_t PyObject_GenericHash(PyObject *obj)

Generic hashing function that is meant to be put into a type object’s tp_hash slot. Its result only depends on the object’s identity.

CPython implementation detail: In CPython, it is equivalent to Py_HashPointer().

Added in version 3.13.