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Idsets API

Specialized set implementations for storing sorted lists of positive integers (document IDs). These are more memory-efficient than the built-in set for certain use cases, though they are slower for most operations since they are pure Python.

Overview

The DocIdSet class is the abstract base class. Concrete implementations include BitSet, OnDiskBitSet, SortedIntSet, RoaringIdSet, and MultiIdSet. The AutoIdSet function selects the best implementation based on the contents.

Module Functions

autoset

whoosh.idsets.autoset

A factory that creates an appropriate DocIdSet subclass based on the contents of a given iterable. If all integers in the set are below 10,000, returns a BitSet; otherwise returns a SortedIntSet.

DocIdSet

class whoosh.idsets.DocIdSet

Abstract base class for set implementations specialized toward storing sorted lists of positive integers.

Inheritance: Inherits from set-like interface.

Methods:

• __eq__(other): Compares two DocIdSet instances by iterating.
• __len__(): Returns the number of elements. Override in subclasses.
• __iter__(): Yields elements in sorted order. Override in subclasses.
• __contains__(i): Returns True if i is in the set.
• __or__(other): Returns self.union(other).
• __and__(other): Returns self.intersection(other).
• __sub__(other): Returns self.difference(other).
• copy(): Returns a copy of this set.
• add(n): Adds n to the set.
• discard(n): Removes n from the set (no error if absent).
• update(other): Adds all elements from other.
• intersection_update(other): Removes elements not in other.
• difference_update(other): Removes all elements in other.
• invert_update(size): In-place inversion over the range [0, size).
• intersection(other): Returns a new set with elements in both.
• union(other): Returns a new set with elements from both.
• difference(other): Returns a new set with elements in self but not other.
• invert(size): Returns a new set that is the inversion over [0, size).
• isdisjoint(other): Returns True if no elements are shared.
• before(i): Returns the previous integer in the set before i, or None.
• after(i): Returns the next integer in the set after i, or None.
• first(): Returns the first (lowest) integer.
• last(): Returns the last (highest) integer.

BaseBitSet

class whoosh.idsets.BaseBitSet(DocIdSet)

Base class for bitmap-backed DocIdSet implementations. Uses a bytes-based bitmap where each bit represents membership of an integer.

Abstract Methods to Override:

• byte_count(): Returns the number of bytes in the bitmap.
• _get_byte(i): Returns the byte at index i.
• _iter_bytes(): Yields all bytes in the bitmap.

Inherited Methods: All DocIdSet methods with efficient bitmap implementations of __len__, __iter__, __contains__, first, and last.

OnDiskBitSet

class whoosh.idsets.OnDiskBitSet(file, doc_count)

A BaseBitSet that reads the bitmap from a file on disk, using mmap for memory efficiency.

Constructor:

• file: A file-like object (opened in binary mode) containing the bitmap.
• doc_count: Total number of documents (bits) represented.

from whoosh.idsets import OnDiskBitSet

with open("deletions.dat", "rb") as f:
    bs = OnDiskBitSet(f, doc_count=10000)
    if 42 in bs:
        print("Document 42 is deleted")

BitSet

class whoosh.idsets.BitSet

A BaseBitSet that stores the bitmap in memory as a bytearray. Fast for membership tests and set operations on small ranges of integers.

Constructor:

• Optional initial iterable of integers.

from whoosh.idsets import BitSet

bs = BitSet([0, 5, 10, 15])
print(5 in bs)  # True
print(bs.first())  # 0
print(len(bs))   # 4

Methods:

• from_blob(data): Create a BitSet from raw bytes.
• tostring(): Returns the bitmap as a bytes string.
• set_reverse(): Prepares the set for reverse iteration.

SortedIntSet

class whoosh.idsets.SortedIntSet

A DocIdSet that stores integers as a sorted list of Python int objects. More memory-efficient than BitSet for sparse sets but slower for membership tests.

Constructor:

• Optional initial iterable of integers.

from whoosh.idsets import SortedIntSet

sis = SortedIntSet([100, 500, 999])
print(500 in sis)  # True
print(sis.after(200))  # 500

ReverseIdSet

class whoosh.idsets.ReverseIdSet(child)

Wraps another DocIdSet to reverse the interpretation of integers. Instead of representing membership directly, the set represents the complement of the inner set. Useful for representing deleted documents.

Constructor:

• child: The DocIdSet to reverse.

Example: If child represents documents {3, 7, 9}, then ReverseIdSet(child) represents all documents except {3, 7, 9}.

RoaringIdSet

class whoosh.idsets.RoaringIdSet

A DocIdSet that partitions integers into 16-bit buckets and uses BitSet within each bucket. More memory-efficient than a single flat BitSet for large, sparse sets of integers.

Constructor:

• Optional initial iterable of integers.

Methods:

• from_bytes(data): Deserialize from bytes.
• to_bytes(): Serialize to bytes.
• to_bytes_list(): Returns a list of (bucket, bytes) pairs.

MultiIdSet

class whoosh.idsets.MultiIdSet(readers, offsets=None)

Combines multiple DocIdSet instances into one, handling document ID offsets automatically. Used for combining deletions across multiple segments.

Constructor:

• readers: List of DocIdSet instances (one per segment).
• offsets: Optional list of base docnum offsets for each reader. If omitted, offsets are computed automatically.

Methods:

• __contains__(i): Checks the appropriate sub-set based on offsets.
• __iter__(): Iterates over all integers in all sub-sets.
• __len__(): Returns the total count across all sub-sets.