BloomPy is a simple bloom filter implementation. A bloom filter is an efficient way to track and test for set membership. It is a probabilistic data structure, with a nonzero false positive rate and a strictly zero false negative rate.
A bloom filter contains an array of m bits, zero-initialized, along with k hash functions, mapping data onto the integers (0,1,...,m-1). When a piece of data is stored in the bloom filter, it is run through each of the hash functions, and the bit in the bloom filter's array corresponding to the result of each hash function is set to 1. To check if a piece of data is in the bloom filter, it is again run through each of the hash functions, and the corresponding array elements are checked; if any are zero, then the data is not in the bloom filter.
BloomPy uses Murmur for hashing, with many thanks to Austin Appleby and Hajime Senuma.
There are plenty of situations where a direct object lookup could be computationally or temporally costly, or otherwise undesirable. Particularly when dealing with complex databases at scale, table inclusion lookups are vastly more expensive than a bloom filter.
For this reason, a particularly popular use case for bloom filters is DDoS defense (see Yi, Yu, Zhou, Hai, and Bonti, page 12); more generally, large automated blacklists or whitelists are a good candidate for bloom filter use.
Clone this repository and run sudo python setup.py install. (Skip the sudo if you're on Windows.)
git clone git@github.com:6C1/BloomPy.git
cd BloomPy
sudo python setup.py install
BloomPy is just one class: BloomFilter.
Make a bloom filter, or make one specifying m, or k, or both:
b = BloomFilter()
c = BloomFilter(8675309)
d = BloomFilter(k=7)
e = BloomFilter(867530,9)
Add some data to the bloom filter:
b.store(moby_dick.text)
b.store("The cake is a Lie algebra")
And verify its membership:
assert moby_dick.text in b
assert "The cake is a Lie algebra" in b
assert "Cheep cheep cheep!" not in b
Wipe it clean to start over:
b.wipe()
This is licensed under the MIT license, both in the LICENSE file in this directory and, hey look! Here's a copy as well.
The MIT License (MIT)
Copyright (c) 2015 Cooper Stimson
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