cdifflib
C implementation of parts of difflib
Decision gist · record as of 2026-08-14
Yes, if you have a performance-critical diffing workload on lists and are willing to accept medium install friction (compiled extension). The package is stable, permissively licensed, has no dependencies, and offers a straightforward 4x speedup. Dormant maintenance is a minor concern but not a blocker—the code is mature and the repo remains reachable. Install only if you've profiled and confirmed difflib is actually your bottleneck.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Input sequences must be lists; non-list iterables are converted to lists automatically, which may cause unexpected memory or performance behavior with very large iterables.
- Medium install friction due to compiled C extension requiring platform-specific wheels.
- The package is dormant (last release 578 days ago) but repo remains active with recent commits; no runtime dependencies simplifies deployment.
License · maintenance · safety
permissive license (permissive) — BSD 2-Clause license (permissive) permits commercial and private use with minimal restrictions—retain copyright notice and disclaimer in distributions.
last release 2025-01-13 (578 days) · last repo commit 2025-01-13 · 41 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 233,173 downloads/mo, #9,042 on PyPI
Alternatives
Verify before relying
from cdifflib import CSequenceMatcher
s = CSequenceMatcher(None, ['a', 'b', 'c'], ['a', 'x', 'c'])
match = s.find_longest_match(0, 3, 0, 3)
print(match) # Match(a=0, b=0, size=1)- Whether prebuilt wheels are available for all modern Python versions and platforms beyond the arm64 macOS wheels listed.
- Current test coverage and whether the package passes on Python 3.13+ given the dormant maintenance status.
- Whether the 4x speedup claim holds for typical real-world use cases or only for specific input patterns.
What it is and what it does
cdifflib is a C-language reimplementation of core parts of Python's standard difflib module, specifically the SequenceMatcher class. It trades the flexibility of generic iterables for raw speed: it only accepts lists as input, but performs sequence matching roughly 4x faster than the pure Python version when processing large data. The API is fully compatible with difflib.SequenceMatcher, so you can drop it in as a replacement—even monkey-patch it into difflib itself to accelerate other libraries that use difflib transparently.
The package has no runtime dependencies and compiles to platform-specific wheels. It is marked Production/Stable and supports Python 3.4 and later, though the project is dormant (last release 578 days ago). The main gotcha is that it requires list inputs; anything else gets converted to a list in the constructor, which can be surprising if you pass generators or other iterables expecting lazy evaluation.
Use it for
- Accelerating diff operations in large-scale text processing pipelines where sequence matching is a bottleneck.
- Speeding up test frameworks or code review tools that compare file contents or code snippets.
- Replacing difflib globally in an application to transparently accelerate any library that depends on difflib.
- Comparing large lists of structured data (records, tokens, etc.) where Python's difflib would be too slow.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes, if you have a performance-critical diffing workload on lists and are willing to accept medium install friction (compiled extension).
The package is stable, permissively licensed, has no dependencies, and offers a straightforward 4x speedup. Dormant maintenance is a minor concern but not a blocker—the code is mature and the repo remains reachable. Install only if you've profiled and confirmed difflib is actually your bottleneck.
Install
cdifflib on PyPI
Before you install
Medium install friction due to compiled C extension requiring platform-specific wheels. The package is dormant (last release 578 days ago) but repo remains active with recent commits; no runtime dependencies simplifies deployment.
Input sequences must be lists; non-list iterables are converted to lists automatically, which may cause unexpected memory or performance behavior with very large iterables.
License in practice
BSD 2-Clause license (permissive) permits commercial and private use with minimal restrictions—retain copyright notice and disclaimer in distributions.
Quickstart
from cdifflib import CSequenceMatcher
s = CSequenceMatcher(None, ['a', 'b', 'c'], ['a', 'x', 'c'])
match = s.find_longest_match(0, 3, 0, 3)
print(match) # Match(a=0, b=0, size=1)Verify before relying
- Whether prebuilt wheels are available for all modern Python versions and platforms beyond the arm64 macOS wheels listed.
- Current test coverage and whether the package passes on Python 3.13+ given the dormant maintenance status.
- Whether the 4x speedup claim holds for typical real-world use cases or only for specific input patterns.
Package facts
| License | permissive license permissive |
| Python support | Supports the current Python release >=3.4 |
| Install friction | Medium. Platform-specific wheel |
| Runtime dependencies | None |
| Maintenance | Dormant 578 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 233,173 / month, #9,042 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | Development Status :: 5 - Production/StableEnvironment :: ConsoleIntended Audience :: DevelopersLicense :: OSI Approved :: BSD LicenseOperating System :: MacOS :: MacOS XOperating System :: Microsoft :: WindowsOperating System :: POSIXProgramming Language :: PythonTopic :: Software DevelopmentTopic :: Text Processing :: General |
Evidence: cdifflib-1.2.9-cp310-cp310-macosx_15_0_arm64.whl; cdifflib-1.2.9-cp311-cp311-macosx_15_0_arm64.whl; cdifflib-1.2.9-cp312-cp312-macosx_15_0_arm64.whl; cdifflib-1.2.9-cp313-cp313-macosx_15_0_arm64.whl; cdifflib-1.2.9-cp39-cp39-macosx_15_0_arm64.whl
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See also cydifflib · fastdiff · pyxDamerauLevenshtein · textdistance · rpm-vercmp · deepdiff · recursive-diff · collate-data-diff · cyseq · tfidf-matcher