CRCmod-plus

2.3.1 · active · verified Mon Apr 13

crcmod-plus is a modernized Python package for generating objects that compute the Cyclic Redundancy Check (CRC). It is a drop-in replacement for the original `crcmod` 1.7 package, having dropped Python 2 support and updated the build pipeline for modern Python environments. It enables the use of any 8, 16, 24, 32, or 64-bit CRC, allowing users to specify custom polynomials or utilize a variety of predefined CRC algorithms. The library maintains a moderate release cadence, primarily focusing on Python compatibility and minor enhancements.

Warnings

breaking crcmod-plus dropped support for Python 2.x. If migrating from the original `crcmod` 1.7, ensure your environment is Python 3.9 or newer.
Fix: Upgrade to Python 3.9+ and install `crcmod-plus`.
gotcha CRC functions and classes in `crcmod-plus` (and `crcmod`) expect byte strings (`bytes`) as input for Python 3.x. Passing Unicode strings (`str`) will result in a TypeError.
Fix: Ensure all input data is encoded to `bytes` (e.g., `my_string.encode('utf-8')`) before passing it to CRC functions.
gotcha While `crcmod-plus` is a drop-in replacement for `crcmod` 1.7, it is a distinct package. Users should explicitly install `crcmod-plus` for the modernized, Python 3-compatible version, as the original `crcmod` on PyPI is old and unmaintained.
Fix: Always use `pip install crcmod-plus` to ensure you are getting the actively maintained and Python 3.9+ compatible version.
gotcha The `crcmod.predefined` module, which contains standard CRC algorithms, needs to be explicitly imported (e.g., `import crcmod.predefined`). Symbols like `mkPredefinedCrcFun` are not directly available under `import crcmod`.
Fix: Always use `import crcmod.predefined` when intending to use predefined CRC algorithms or classes.

Install

pip install crcmod-plus Install latest version

Imports

mkCrcFun

import crcmod
crc_func = crcmod.mkCrcFun(...)

Crc
```
import crcmod
crc_obj = crcmod.Crc(...)
```
mkPredefinedCrcFun
```
import crcmod.predefined
predefined_crc_func = crcmod.predefined.mkPredefinedCrcFun('crc-32')
```
Predefined CRC functions are in the `crcmod.predefined` submodule, not directly under `crcmod`.
PredefinedCrc
```
import crcmod.predefined
predefined_crc_obj = crcmod.predefined.PredefinedCrc('crc-32')
```
The `PredefinedCrc` class is in the `crcmod.predefined` submodule, not directly under `crcmod`.

Quickstart

This quickstart demonstrates how to calculate CRCs using both custom polynomials via `crcmod.mkCrcFun` and `crcmod.Crc` class, and predefined algorithms via `crcmod.predefined.mkCrcFun` and `crcmod.predefined.PredefinedCrc` class.

import crcmod
import crcmod.predefined

# --- Custom CRC-32 calculation ---
# Create a CRC function using a custom polynomial (e.g., CRC-32-ISO-HDLC)
crc32_func_custom = crcmod.mkCrcFun(0x104C11DB7, initCrc=0, xorOut=0xFFFFFFFF)
data_bytes = b"123456789"
crc_value_custom = crc32_func_custom(data_bytes)
print(f"Custom CRC-32 for '123456789': {hex(crc_value_custom)}")

# Alternatively, use the Crc class for a stateful calculator
crc32_obj_custom = crcmod.Crc(0x104C11DB7, initCrc=0, xorOut=0xFFFFFFFF)
crc32_obj_custom.update(b"123")
crc32_obj_custom.update(b"456789")
print(f"Custom CRC-32 (Crc class) for '123456789': {hex(crc32_obj_custom.crcValue)}")

# --- Predefined CRC-16 (XMODEM) calculation ---
# Create a CRC function using a predefined algorithm name
crc16_func_xmodem = crcmod.predefined.mkCrcFun('xmodem')
crc_value_xmodem = crc16_func_xmodem(data_bytes)
print(f"Predefined CRC-16 (XMODEM) for '123456789': {hex(crc_value_xmodem)}")

# Alternatively, use the PredefinedCrc class
crc16_obj_xmodem = crcmod.predefined.PredefinedCrc('xmodem')
crc16_obj_xmodem.update(data_bytes)
print(f"Predefined CRC-16 (XMODEM, PredefinedCrc class) for '123456789': {hex(crc16_obj_xmodem.crcValue)}")

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