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# -*- encoding: utf-8 -*-
"""This module implements a bloom filter probabilistic data structure and
an a Scalable Bloom Filter that grows in size as your add more items to it
without increasing the false positive error_rate.
Requires the bitarray library: http://pypi.python.org/pypi/bitarray/
>>> from pybloom import BloomFilter
>>> f = BloomFilter(capacity=10000, error_rate=0.001)
>>> for i in range_fn(0, f.capacity):
... _ = f.add(i)
...
>>> 0 in f
True
>>> f.capacity in f
False
>>> len(f) <= f.capacity
True
>>> (1.0 - (len(f) / float(f.capacity))) <= f.error_rate + 2e-18
True
>>> from pybloom import ScalableBloomFilter
>>> sbf = ScalableBloomFilter(mode=ScalableBloomFilter.SMALL_SET_GROWTH)
>>> count = 10000
>>> for i in range_fn(0, count):
... _ = sbf.add(i)
...
>>> sbf.capacity > count
True
>>> len(sbf) <= count
True
>>> (1.0 - (len(sbf) / float(count))) <= sbf.error_rate + 2e-18
True
"""
from __future__ import absolute_import
import math
import hashlib
from pybloom.utils import range_fn, is_string_io, running_python_3
from struct import unpack, pack, calcsize
try:
import bitarray
except ImportError:
raise ImportError('pybloom requires bitarray >= 0.3.4')
__version__ = '2.0'
__author__ = "Jay Baird <jay.baird@me.com>, Bob Ippolito <bob@redivi.com>,\
Marius Eriksen <marius@monkey.org>,\
Alex Brasetvik <alex@brasetvik.com>,\
Matt Bachmann <bachmann.matt@gmail.com>,\
"
def make_hashfuncs(num_slices, num_bits):
if num_bits >= (1 << 31):
fmt_code, chunk_size = 'Q', 8
elif num_bits >= (1 << 15):
fmt_code, chunk_size = 'I', 4
else:
fmt_code, chunk_size = 'H', 2
total_hash_bits = 8 * num_slices * chunk_size
if total_hash_bits > 384:
hashfn = hashlib.sha512
elif total_hash_bits > 256:
hashfn = hashlib.sha384
elif total_hash_bits > 160:
hashfn = hashlib.sha256
elif total_hash_bits > 128:
hashfn = hashlib.sha1
else:
hashfn = hashlib.md5
fmt = fmt_code * (hashfn().digest_size // chunk_size)
num_salts, extra = divmod(num_slices, len(fmt))
if extra:
num_salts += 1
salts = tuple(hashfn(hashfn(pack('I', i)).digest()) for i in range_fn(num_salts))
def _make_hashfuncs(key):
if running_python_3:
if isinstance(key, str):
key = key.encode('utf-8')
else:
key = str(key).encode('utf-8')
else:
if isinstance(key, unicode):
key = key.encode('utf-8')
else:
key = str(key)
i = 0
for salt in salts:
h = salt.copy()
h.update(key)
for uint in unpack(fmt, h.digest()):
yield uint % num_bits
i += 1
if i >= num_slices:
return
return _make_hashfuncs
class BloomFilter(object):
FILE_FMT = b'<dQQQQ'
def __init__(self, capacity, error_rate=0.001):
"""Implements a space-efficient probabilistic data structure
capacity
this BloomFilter must be able to store at least *capacity* elements
while maintaining no more than *error_rate* chance of false
positives
error_rate
the error_rate of the filter returning false positives. This
determines the filters capacity. Inserting more than capacity
elements greatly increases the chance of false positives.
>>> b = BloomFilter(capacity=100000, error_rate=0.001)
>>> b.add("test")
False
>>> "test" in b
True
"""
if not (0 < error_rate < 1):
raise ValueError("Error_Rate must be between 0 and 1.")
if not capacity > 0:
raise ValueError("Capacity must be > 0")
# given M = num_bits, k = num_slices, P = error_rate, n = capacity
# k = log2(1/P)
# solving for m = bits_per_slice
# n ~= M * ((ln(2) ** 2) / abs(ln(P)))
# n ~= (k * m) * ((ln(2) ** 2) / abs(ln(P)))
# m ~= n * abs(ln(P)) / (k * (ln(2) ** 2))
num_slices = int(math.ceil(math.log(1.0 / error_rate, 2)))
bits_per_slice = int(math.ceil(
(capacity * abs(math.log(error_rate))) /
(num_slices * (math.log(2) ** 2))))
self._setup(error_rate, num_slices, bits_per_slice, capacity, 0)
self.bitarray = bitarray.bitarray(self.num_bits, endian='little')
self.bitarray.setall(False)
def _setup(self, error_rate, num_slices, bits_per_slice, capacity, count):
self.error_rate = error_rate
self.num_slices = num_slices
self.bits_per_slice = bits_per_slice
self.capacity = capacity
self.num_bits = num_slices * bits_per_slice
self.count = count
self.make_hashes = make_hashfuncs(self.num_slices, self.bits_per_slice)
def __contains__(self, key):
"""Tests a key's membership in this bloom filter.
>>> b = BloomFilter(capacity=100)
>>> b.add("hello")
False
>>> "hello" in b
True
"""
bits_per_slice = self.bits_per_slice
bitarray = self.bitarray
hashes = self.make_hashes(key)
offset = 0
for k in hashes:
if not bitarray[offset + k]:
return False
offset += bits_per_slice
return True
def __len__(self):
"""Return the number of keys stored by this bloom filter."""
return self.count
def add(self, key, skip_check=False):
""" Adds a key to this bloom filter. If the key already exists in this
filter it will return True. Otherwise False.
>>> b = BloomFilter(capacity=100)
>>> b.add("hello")
False
>>> b.add("hello")
True
>>> b.count
1
"""
bitarray = self.bitarray
bits_per_slice = self.bits_per_slice
hashes = self.make_hashes(key)
found_all_bits = True
if self.count > self.capacity:
raise IndexError("BloomFilter is at capacity")
offset = 0
for k in hashes:
if not skip_check and found_all_bits and not bitarray[offset + k]:
found_all_bits = False
self.bitarray[offset + k] = True
offset += bits_per_slice
if skip_check:
self.count += 1
return False
elif not found_all_bits:
self.count += 1
return False
else:
return True
def copy(self):
"""Return a copy of this bloom filter.
"""
new_filter = BloomFilter(self.capacity, self.error_rate)
new_filter.bitarray = self.bitarray.copy()
return new_filter
def union(self, other):
""" Calculates the union of the two underlying bitarrays and returns
a new bloom filter object."""
if self.capacity != other.capacity or \
self.error_rate != other.error_rate:
raise ValueError("Unioning filters requires both filters to have \
both the same capacity and error rate")
new_bloom = self.copy()
new_bloom.bitarray = new_bloom.bitarray | other.bitarray
return new_bloom
def __or__(self, other):
return self.union(other)
def intersection(self, other):
""" Calculates the intersection of the two underlying bitarrays and returns
a new bloom filter object."""
if self.capacity != other.capacity or \
self.error_rate != other.error_rate:
raise ValueError("Intersecting filters requires both filters to \
have equal capacity and error rate")
new_bloom = self.copy()
new_bloom.bitarray = new_bloom.bitarray & other.bitarray
return new_bloom
def __and__(self, other):
return self.intersection(other)
def tofile(self, f):
"""Write the bloom filter to file object `f'. Underlying bits
are written as machine values. This is much more space
efficient than pickling the object."""
f.write(pack(self.FILE_FMT, self.error_rate, self.num_slices,
self.bits_per_slice, self.capacity, self.count))
(f.write(self.bitarray.tobytes()) if is_string_io(f)
else self.bitarray.tofile(f))
@classmethod
def fromfile(cls, f, n=-1):
"""Read a bloom filter from file-object `f' serialized with
``BloomFilter.tofile''. If `n' > 0 read only so many bytes."""
headerlen = calcsize(cls.FILE_FMT)
if 0 < n < headerlen:
raise ValueError('n too small!')
filter = cls(1) # Bogus instantiation, we will `_setup'.
filter._setup(*unpack(cls.FILE_FMT, f.read(headerlen)))
filter.bitarray = bitarray.bitarray(endian='little')
if n > 0:
(filter.bitarray.frombytes(f.read(n-headerlen)) if is_string_io(f)
else filter.bitarray.fromfile(f, n - headerlen))
else:
(filter.bitarray.frombytes(f.read()) if is_string_io(f)
else filter.bitarray.fromfile(f))
if filter.num_bits != filter.bitarray.length() and \
(filter.num_bits + (8 - filter.num_bits % 8)
!= filter.bitarray.length()):
raise ValueError('Bit length mismatch!')
return filter
def __getstate__(self):
d = self.__dict__.copy()
del d['make_hashes']
return d
def __setstate__(self, d):
self.__dict__.update(d)
self.make_hashes = make_hashfuncs(self.num_slices, self.bits_per_slice)
class ScalableBloomFilter(object):
SMALL_SET_GROWTH = 2 # slower, but takes up less memory
LARGE_SET_GROWTH = 4 # faster, but takes up more memory faster
FILE_FMT = '<idQd'
def __init__(self, initial_capacity=100, error_rate=0.001,
mode=SMALL_SET_GROWTH):
"""Implements a space-efficient probabilistic data structure that
grows as more items are added while maintaining a steady false
positive rate
initial_capacity
the initial capacity of the filter
error_rate
the error_rate of the filter returning false positives. This
determines the filters capacity. Going over capacity greatly
increases the chance of false positives.
mode
can be either ScalableBloomFilter.SMALL_SET_GROWTH or
ScalableBloomFilter.LARGE_SET_GROWTH. SMALL_SET_GROWTH is slower
but uses less memory. LARGE_SET_GROWTH is faster but consumes
memory faster.
>>> b = ScalableBloomFilter(initial_capacity=512, error_rate=0.001, \
mode=ScalableBloomFilter.SMALL_SET_GROWTH)
>>> b.add("test")
False
>>> "test" in b
True
>>> unicode_string = u'¡'
>>> b.add(unicode_string)
False
>>> unicode_string in b
True
"""
if not error_rate or error_rate < 0:
raise ValueError("Error_Rate must be a decimal less than 0.")
self._setup(mode, 0.9, initial_capacity, error_rate)
self.filters = []
def _setup(self, mode, ratio, initial_capacity, error_rate):
self.scale = mode
self.ratio = ratio
self.initial_capacity = initial_capacity
self.error_rate = error_rate
def __contains__(self, key):
"""Tests a key's membership in this bloom filter.
>>> b = ScalableBloomFilter(initial_capacity=100, error_rate=0.001, \
mode=ScalableBloomFilter.SMALL_SET_GROWTH)
>>> b.add("hello")
False
>>> "hello" in b
True
"""
for f in reversed(self.filters):
if key in f:
return True
return False
def add(self, key):
"""Adds a key to this bloom filter.
If the key already exists in this filter it will return True.
Otherwise False.
>>> b = ScalableBloomFilter(initial_capacity=100, error_rate=0.001, \
mode=ScalableBloomFilter.SMALL_SET_GROWTH)
>>> b.add("hello")
False
>>> b.add("hello")
True
"""
if key in self:
return True
if not self.filters:
filter = BloomFilter(
capacity=self.initial_capacity,
error_rate=self.error_rate * (1.0 - self.ratio))
self.filters.append(filter)
else:
filter = self.filters[-1]
if filter.count >= filter.capacity:
filter = BloomFilter(
capacity=filter.capacity * self.scale,
error_rate=filter.error_rate * self.ratio)
self.filters.append(filter)
filter.add(key, skip_check=True)
return False
@property
def capacity(self):
"""Returns the total capacity for all filters in this SBF"""
return sum(f.capacity for f in self.filters)
@property
def count(self):
return len(self)
def tofile(self, f):
"""Serialize this ScalableBloomFilter into the file-object
`f'."""
f.write(pack(self.FILE_FMT, self.scale, self.ratio,
self.initial_capacity, self.error_rate))
# Write #-of-filters
f.write(pack(b'<l', len(self.filters)))
if len(self.filters) > 0:
# Then each filter directly, with a header describing
# their lengths.
headerpos = f.tell()
headerfmt = b'<' + b'Q'*(len(self.filters))
f.write(b'.' * calcsize(headerfmt))
filter_sizes = []
for filter in self.filters:
begin = f.tell()
filter.tofile(f)
filter_sizes.append(f.tell() - begin)
f.seek(headerpos)
f.write(pack(headerfmt, *filter_sizes))
@classmethod
def fromfile(cls, f):
"""Deserialize the ScalableBloomFilter in file object `f'."""
filter = cls()
filter._setup(*unpack(cls.FILE_FMT, f.read(calcsize(cls.FILE_FMT))))
nfilters, = unpack(b'<l', f.read(calcsize(b'<l')))
if nfilters > 0:
header_fmt = b'<' + b'Q'*nfilters
bytes = f.read(calcsize(header_fmt))
filter_lengths = unpack(header_fmt, bytes)
for fl in filter_lengths:
filter.filters.append(BloomFilter.fromfile(f, fl))
else:
filter.filters = []
return filter
def __len__(self):
"""Returns the total number of elements stored in this SBF"""
return sum(f.count for f in self.filters)
if __name__ == "__main__":
import doctest
doctest.testmod()
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