This module provides an IndexedBzip2File class, which can be used to seek inside bzip2 files without having to decompress them first.
It's based on an improved version of the bzip2 decoder bzcat from toybox, which was refactored and extended to be able to export an import bzip2 block offsets and seek to them.
Seeking inside a block is only emulated, so IndexedBzip2File will only speed up seeking when there are more than one blocks, which should almost always be the cause for archives larger than 1 MB.
You can simply install it from PyPI:
pip install indexed_bzip2
fromindexed_bzip2importIndexedBzip2Filefile=IndexedBzip2File("example.bz2")# You can now use it like a normal filefile.seek(123)data=file.read(100)
The first call to seek will ensure that the block offset list is complete and therefore might create them first.
Because of this the first call to seek might take a while.
The creation of the list of bzip2 blocks can take a while because it has to decode the bzip2 file completely.
To avoid this setup when opening a bzip2 file, the block offset list can be exported and imported.
fromindexed_bzip2importIndexedBzip2Filefile=IndexedBzip2File("example.bz2")blockOffsets=file.blockOffsets()# can take a whilefile.close()file2=IndexedBzip2File("example.bz2")blockOffsets=file2.setBlockOffsets(blockOffsets)# should be fastfile2.seek(123)data=file2.read(100)file2.close()