Python bindings for CityHash and FarmHash
Project description
A Python wrapper around FarmHash and CityHash
Getting Started
To use this package in your program, simply type
pip install cityhash
After that, you should be able to import the module and do things with it (see usage example below).
Usage Examples
Stateless Hashing
The package contains 64- and 128-bit implementations of the CityHash algorithm, named as follows:
>>> from cityhash import CityHash32, CityHash64, CityHash128
>>> print(CityHash32("abc"))
795041479
>>> print(CityHash64("abc"))
2640714258260161385
>>> print(CityHash128("abc"))
76434233956484675513733017140465933893
Hardware-independent Fingerprints
Fingerprints are seedless hashes which are guaranteed to be hardware- and platform- independent.
>>> from farmhash import Fingerprint128
>>> print(Fingerprint128("abc"))
76434233956484675513733017140465933893
Incremental Hashing
this implementation of CityHash and FarmHash does not support incremental hashing. If you require this feature, use MetroHash instead, which does support it.
Fast Hashing of NumPy Arrays
The methods in this module support Python Buffer Protocol, which allows them to be used on any object that exports a buffer interface. Here is an example showing hashing of a 4D NumPy array:
>>> import numpy as np
>>> from farmhash import FarmHash64
>>> arr = np.zeros((256, 256, 4))
>>> FarmHash64(arr)
1550282412043536862
Note that arrays need to be contiguous for this to work. To convert a non-contiguous array, use np.ascontiguousarray() method.
SSE4.2 Optimizations
On CPUs that support SSE4.2 instruction set, optimized FarmHash has significant advantage over non-optimized version and over CityHash, as can be seen below. The numbers below were recoreded on a 2.4 GHz Intel Xeon CPU (E5-2620), and the task was to hash a 512x512x3 NumPy array.
Method |
Time (best of 3) |
---|---|
FarmHash64 / SSE4.2 |
378 µs ± 43.4 µs |
FarmHash64 |
489 µs ± 13.7 µs |
CityHash64 |
499 µs ± 17.2 µs |
Currently, the setup.py script automatically detects whether the CPU supports SSE4.2 instruction set and enables it during the compilation phase if it does.
Development
For those who want to contribute, here is a quick start using some makefile commands:
git clone https://github.com/escherba/python-cityhash.git
cd python-cityhash
make env # creates a Python virtualenv
make test # run Python tests
make cpp-test # run C++ tests
The Makefiles provided have self-documenting targets. To find out which targets are available, type:
make help
See Also
For other fast non-cryptographic hashing implementations available as Python extensions, see MetroHash and MurmurHash.
License
This software is licensed under the MIT License. See the included LICENSE file for details.
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