crc32c

library2.9pypypi✓ verified 26d ago

The `crc32c` Python package provides an implementation of the CRC32C checksum algorithm, intelligently leveraging hardware acceleration (Intel SSE 4.2, ARMv8 crc32 instructions) when available, and falling back to an optimized software implementation otherwise. As of version 2.8, it offers robust data integrity verification across various platforms. The library aims for regular updates.

serialization

pip install crc32c

github ↗package ↗changelog ↗

INSTALL

IMPORT

SIG · CRC32C

crc32c

serializationpythonv2.9

Install

1.7s avg

Import

113ms

Disk

16MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v2.9 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

py 3.10–3.95 runs

installs and imports cleanly · install 0.0s · import 0.118s · 18MB

glibc

py 3.10–3.95 runs

installs and imports cleanly · install 1.7s · import 0.108s · 19MB

16MB installed

● package 16MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

crc32c

✓ import crc32c

Main module import

crc32c

✓ crc32c.crc32c(data)

✗ crc32c.crc32(data)

The 'crc32c.crc32' function is deprecated; use 'crc32c.crc32c' instead for the core checksum calculation.

CRC32CHash

✓ from crc32c import CRC32CHash

For streaming checksum calculations with a hash-like object.

Demonstrates basic CRC32C calculation, incremental updates, usage of the `CRC32CHash` object, and how to check for hardware acceleration.

import crc32c # Calculate CRC32C for a byte string data = b"hello world" checksum = crc32c.crc32c(data) print(f"CRC32C checksum of '{data.decode()}': {checksum}") # Incremental calculation (similar to binascii.crc32 with 'value' parameter) crc_part1 = crc32c.crc32c(b"hello") crc_total = crc32c.crc32c(b" world", value=crc_part1) print(f"Incremental CRC32C: {crc_total}") # Using the hash-like object hash_obj = crc32c.CRC32CHash() hash_obj.update(b"hello") hash_obj.update(b" world") print(f"CRC32CHash object checksum: {hash_obj.checksum}") # Check if hardware acceleration is in use print(f"Hardware acceleration in use: {crc32c.hardware_based}")

Debug

Known issues

deprecatedThe `crc32c.crc32` function is deprecated and will be removed in future versions. Users should switch to `crc32c.crc32c` for all checksum calculations.

fix

Replace `crc32c.crc32(...)` with `crc32c.crc32c(...)`.

affects: <=2.8

gotchaThe `auto` value for the `CRC32C_SW_MODE` environment variable, which controls software fallback behavior, is planned for discontinuation. It's recommended to explicitly use `force` or `none` if specific fallback control is needed.

fix

If setting `CRC32C_SW_MODE`, use `force` to always use software implementation or `none` to raise an error if hardware is unavailable, instead of `auto`.

affects: All versions

breakingIn versions up to 2.6, an `ImportError` was raised if no hardware support was found and software fallback was not enabled. As of version 2.7, this behavior has changed: `CRC32C_SW_MODE='none'` will now issue a `RuntimeWarning` on import and a `RuntimeError` on execution if hardware support is missing.

fix

Update exception handling for `crc32c` import/execution to catch `RuntimeWarning` or `RuntimeError` when `CRC32C_SW_MODE='none'` is set, instead of `ImportError`.

affects: >=2.7 (breaking change from <=2.6)

gotchaThe project uses specific `gcc`/`clang` compiler extensions. If installing from source (e.g., when no pre-built wheel is available for your platform/Python version), older compiler versions might fail to build the package.

fix

Ensure your C/C++ compiler (gcc/clang/Visual Studio) is up-to-date and supports modern extensions. Using a platform with pre-built binary wheels from PyPI is the easiest way to avoid this.

affects: All versions (when building from source)

Errors

Common errors & fixes

ModuleNotFoundError: No module named 'crc32c'

The `crc32c` package is either not installed in the current Python environment, or there's a conflict with other similarly named libraries, or the `brew install crc32c` command installed a C library, not the Python package.

fix

Ensure the Python package is installed using pip: `pip install crc32c`. Verify you are in the correct Python environment. If `google-crc32c` is also installed and causing conflicts, try managing dependencies carefully or isolating environments.

AttributeError: module 'crc32c' has no attribute 'crc32'

The `crc32` function name is deprecated in `crc32c` versions 2.x and later, in favor of `crc32c` (lowercase).

fix

Update your code to use the `crc32c()` function instead of the deprecated `crc32()` function: `import crc32c; checksum = crc32c.crc32c(data)`.

RuntimeError: No hardware crc32c support found and CRC32C_SW_MODE is 'none'

This error occurs when the `CRC32C_SW_MODE` environment variable is explicitly set to 'none', preventing the library from falling back to a software implementation if hardware CRC32C support is not detected on the CPU.

fix

Either ensure your CPU has hardware CRC32C support (Intel SSE 4.2 or ARMv8 crc32 instructions), or allow the software fallback by unsetting `CRC32C_SW_MODE` or setting it to 'auto' or 'force'. Example: `export CRC32C_SW_MODE=force` (before running your Python script).

ERROR: Could not build wheels for crc32c which use PEP 517 and cannot be installed directly

This issue typically arises during installation when pre-built binary wheels are not available for your specific Python version and operating system, and the system lacks the necessary C compiler and development headers to compile the `crc32c` C extension from source.

fix

Install the required build tools for your operating system (e.g., `build-essential` on Debian/Ubuntu, Xcode Command Line Tools on macOS, or Visual Studio Build Tools on Windows). Alternatively, try installing a specific version for which a wheel might exist, or ensure you are on a widely supported platform/Python version.

Upgrade

Version history

2.9latest on PyPI · released Aug 21, 2026

Audit

Dependencies

No dependency data recorded yet.

Agent activity

30 hits · last 30 days

node

Resources

githubhttps://github.com/ICRAR/crc32c ↗

packagehttps://pypi.org/project/crc32c/ ↗

changeloghttps://github.com/ICRAR/crc32c/blob/master/CHANGELOG.md ↗