dlen

Check how long your functions and classes are.

A long function is the cheapest smell to detect and the most reliable one to act on. dlen tells you which ones crossed the line, and where.

$ dlen src/
src/importer.py:42:1: DL001 function 'process_batch' is 34 lines (max 20)
src/importer.py:88:5: DL001 function 'validate' is 14 lines (warn 12)
src/models.py:7:1: DL002 class 'LegacyRecord' is 812 lines (max 500)

Install

uv tool install dlen     # or: pipx install dlen, pip install dlen

Python 3.10 or newer. No dependencies.

Use

dlen src/ tests/                 # files, directories, or both
dlen . --max-function 30         # your project, your thresholds
dlen . --output-format=json      # for other tools

A function's length includes its decorators — they are part of what you read before you understand it.

Exit codes

Warnings never fail the build. That is the point of having two thresholds: one to nudge, one to stop.

Rules

In CI

--output-format=github puts each finding on the diff of the pull request instead of burying it in a log:

- run: uvx dlen src --output-format=github

As a library

The core returns data and prints nothing, so you can build your own reporting on it:

from pathlib import Path
from dlen import Limits, check_paths

findings = check_paths([Path("src")], Limits(max_function=30))
for finding in findings:
    print(finding.code, finding.path, finding.line, finding.message)

Every call returns a fresh list. Two runs never see each other's findings.

How it measures

dlen parses your code with Python's own ast module, so it agrees with Python about what a function is. It sees async def, decorators, nested functions and methods, and it is not fooled by the word def inside a string or a comment.

Versions before 0.1.0 matched text with regular expressions and had been broken on Python 3 since 2017. 0.1.0 is a rewrite: the counts are now correct rather than compatible, and the output carries file, line and column.

Licence

MIT.