Install & Compatibility
Where this runs
tested against v2.3.1 · 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
muslpy 3.10–3.95 runs
installs and imports cleanly · install 0.0s · import 0.014s · 17.9MB
glibcpy 3.10–3.95 runs
installs and imports cleanly · install 1.6s · import 0.014s · 18MB
16MB installed
● package 16MB
Code
Verified usage
Verified import paths — ran on the pinned version, not inferred.
mkCrcFun
✓ from crcmod import mkCrcFun
✗ import crcmod
Crc
✓ from crcmod import Crc
✗ import crcmod
crcmod
✓ from crcmod import crcmod
✗ import crcmod
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)}")
Debug
Known issues
breakingcrcmod-plus dropped support for Python 2.x. If migrating from the original `crcmod` 1.7, ensure your environment is Python 3.9 or newer.fixUpgrade to Python 3.9+ and install `crcmod-plus`.
affects: <2.0.0 (original `crcmod`) -> 2.0.0+
gotchaCRC 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.fixEnsure all input data is encoded to `bytes` (e.g., `my_string.encode('utf-8')`) before passing it to CRC functions. affects: 2.0.0+
gotchaWhile `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.fixAlways use `pip install crcmod-plus` to ensure you are getting the actively maintained and Python 3.9+ compatible version.
affects: All versions
gotchaThe `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`.fixAlways use `import crcmod.predefined` when intending to use predefined CRC algorithms or classes.
affects: All versions, especially before 2.3.1 if relying on implicit side-effects
Upgrade
Version history
2.3.1latest on PyPI · released Oct 10, 2025
Audit
Dependencies
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