CyDifflib

1.2.0 verified Fri May 01 auth: no python

A fast Cython-powered implementation of Python's difflib algorithms (SequenceMatcher, unified_diff, etc.). Current version: 1.2.0. Released irregularly, maintained by the RapidFuzz project. Requires Python >=3.9.

pip install cydifflib

Common errors

error ImportError: cannot import name 'SequenceMatcher' from 'cydifflib' ↓

cause The module is not installed or you're using a very old version that had a different API (pre-1.0).

fix

Run 'pip install --upgrade cydifflib' to get the latest version.

error AttributeError: 'SequenceMatcher' object has no attribute 'get_grouped_opcodes' ↓

cause CyDifflib's SequenceMatcher does not implement all methods from stdlib difflib.

fix

Use difflib.SequenceMatcher if you need get_grouped_opcodes or other missing methods.

error TypeError: Expected str, got bytes ↓

cause CyDifflib expects string inputs, not bytes. It does not handle bytes automatically.

fix

Decode bytes to str before passing: e.g., a = my_bytes.decode('utf-8')

Warnings

gotcha CyDifflib's SequenceMatcher is NOT a drop-in replacement for difflib.SequenceMatcher. It has fewer methods (e.g., no get_grouped_opcodes, real_quick_ratio) and behavior may differ slightly. ↓

fix Check the README for supported features. If you need full compatibility, use difflib instead.

gotcha The library may fail to compile from source if you have an incompatible Cython version or missing build tools. Pre-built wheels are available for most platforms, but not all. ↓

fix Install pre-built wheels from PyPI. If building from source, ensure Cython and a C compiler are installed. Consider using rapidfuzz as a fallback.

deprecated The cydifflib.SequenceMatcher object does not support autojunk parameter (ignored). This behavior is deprecated and will be removed in a future version. ↓

fix Avoid using autojunk parameter or expect it to be ignored. Future versions may raise an error.

Imports

SequenceMatcher
wrong
```
from difflib import SequenceMatcher
```
correct
```
from cydifflib import SequenceMatcher
```
The stdlib difflib.SequenceMatcher is different; cydifflib.SequenceMatcher is specialized and faster.
unified_diff
wrong
```
from difflib import unified_diff
```
correct
```
from cydifflib import unified_diff
```
Similarly, cydifflib.unified_diff returns a generator of strings, while stdlib returns a generator of strings (same API but faster).

Quickstart

Compute similarity between two strings using SequenceMatcher.

from cydifflib import SequenceMatcher
a = "hello world"
b = "hello earth"
sm = SequenceMatcher(None, a, b)
ratio = sm.ratio()
print(f"Similarity: {ratio:.2f}")