cbitstruct
Faster C implementation of bitstruct
Decision gist · record as of 2026-08-14
Yes, if you are already using bitstruct and have identified bit packing/unpacking as a bottleneck in a CPython application on x86_64 Linux. The performance gains are substantial, and the API compatibility makes migration straightforward. No, if you need portability to other architectures, big-endian systems, or non-CPython implementations, or if you require clear error messages and full bitstruct feature parity. The copyleft license (MPL-2.0) also requires careful review if you plan to distribute derived works.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires CPython 3.8 or later; C extension wheels are available only for x86_64 Linux (manylinux2014 and later); other platforms or architectures require compilation from source.
- Medium install friction due to compiled C extension wheels; prebuilt binaries are available for Python 3.8–3.14 on x86_64 Linux, but the package is aging (last release 186 days ago) with modest maintenance activity.
License · maintenance · safety
MPL-2.0 (copyleft) — Licensed under MPL-2.0 (copyleft); derivative works and modifications must be distributed under the same license, which may restrict commercial or proprietary use without disclosure.
last release 2026-02-09 (186 days) · last repo commit 2026-02-09 · 25 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 223,422 downloads/mo, #9,245 on PyPI
Alternatives
Verify before relying
pip install cbitstruct
import cbitstruct
# Pack integers into bits
packed = cbitstruct.pack('u8', 1)
# Unpack bits back to integers
unpacked = cbitstruct.unpack('u8', packed)- Whether the performance gains reported in the test suite (ranging from 8× to 139× faster) hold for real-world workloads outside the benchmark.
- Whether the 64-bit field limit and potential big-endian architecture issues affect your use case.
- Current maintenance trajectory and whether limitations listed as 'Maybe' or 'Probably not' are likely to be addressed.
What it is and what it does
cbitstruct is a C-based reimplementation of the bitstruct library, designed to parse and serialize binary data (bit fields, packed structs, protocol messages) much faster than the pure-Python version. It provides the same API—pack, unpack, pack_into, unpack_from, and compiled format objects—so you can often swap it in as a drop-in replacement by changing the import statement.
The tradeoff is that cbitstruct has real limitations: fields are capped at 64 bits (except padding), it only runs on CPython, error messages are less helpful, and it may not work on big-endian systems. The description notes that exceptions differ from bitstruct and some limitations are unlikely to be lifted. It's best suited for performance-critical code paths where you're already familiar with bitstruct and need the speed boost.
Use it for
- Parsing binary network protocols or packet formats where speed matters and fields fit within 64 bits.
- Serializing structured data into compact binary form for storage or transmission in latency-sensitive applications.
- Unpacking embedded device telemetry or sensor data streams with high throughput requirements.
- Building compiled format objects for repeated pack/unpack cycles in tight loops.
- Migrating performance-critical bitstruct code to C acceleration without rewriting the logic.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes, if you are already using bitstruct and have identified bit packing/unpacking as a bottleneck in a CPython application on x86_64 Linux.
The performance gains are substantial, and the API compatibility makes migration straightforward. No, if you need portability to other architectures, big-endian systems, or non-CPython implementations, or if you require clear error messages and full bitstruct feature parity. The copyleft license (MPL-2.0) also requires careful review if you plan to distribute derived works.
Install
cbitstruct on PyPI
Before you install
Medium install friction due to compiled C extension wheels; prebuilt binaries are available for Python 3.8–3.14 on x86_64 Linux, but the package is aging (last release 186 days ago) with modest maintenance activity.
Requires CPython 3.8 or later; C extension wheels are available only for x86_64 Linux (manylinux2014 and later); other platforms or architectures require compilation from source.
License in practice
Licensed under MPL-2.0 (copyleft); derivative works and modifications must be distributed under the same license, which may restrict commercial or proprietary use without disclosure.
Quickstart
pip install cbitstruct
import cbitstruct
# Pack integers into bits
packed = cbitstruct.pack('u8', 1)
# Unpack bits back to integers
unpacked = cbitstruct.unpack('u8', packed)Verify before relying
- Whether the performance gains reported in the test suite (ranging from 8× to 139× faster) hold for real-world workloads outside the benchmark.
- Whether the 64-bit field limit and potential big-endian architecture issues affect your use case.
- Current maintenance trajectory and whether limitations listed as 'Maybe' or 'Probably not' are likely to be addressed.
Package facts
| License | MPL-2.0 copyleft |
| Python support | Supports the current Python release >=3.8 |
| Install friction | Medium. Platform-specific wheel |
| Runtime dependencies | None |
| Maintenance | Aging 186 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 223,422 / month, #9,245 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | License :: OSI Approved :: Mozilla Public License 2.0 (MPL 2.0)Operating System :: OS IndependentProgramming Language :: CProgramming Language :: Python :: 3 |
Evidence: cbitstruct-1.2.0-cp310-cp310-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl; cbitstruct-1.2.0-cp311-cp311-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl; cbitstruct-1.2.0-cp312-cp312-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl; cbitstruct-1.2.0-cp313-cp313-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl; cbitstruct-1.2.0-cp314-cp314-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl; cbitstruct-1.2.0-cp38-cp38-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl; cbitstruct-1.2.0-cp39-cp39-manylinux2014_x86_64.manylinux_2_17_x86_64.manylinux_2_28_x86_64.whl
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See also bitstruct · plum-py · bitstring · pycstruct · dissect.cstruct · tibs · msgpack · bitarray · fdt · PyByteBuffer