CPITD: Copy Paste Is The Devil

A static code analysis tool that rakes you over the coals for using copy/paste. Because copy/paste is the devil. Language agnostic, and blazingly fast.

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Installation

pip install cpitd

Requires Python 3.10+.

Development

For development (linting, tests, docs):

git clone https://github.com/scythia-marrow/cpitd.git
cd cpitd
python -m venv venv
source venv/bin/activate
pip install -e ".[dev]"
pre-commit install

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Quick Start

# Scan current directory
cpitd

# Scan specific paths
cpitd src/ lib/

# JSON output for CI pipelines
cpitd --format json src/ | jq '.[]'

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Configuration

Settings can live in pyproject.toml so you don't repeat yourself on every invocation:

[tool.cpitd]
format = "human"
ignore = ["tests/fixtures/*", "vendor/*"]
suppress = ["*@abstractmethod*"]

CLI flags always override file config. For list options (ignore, suppress, languages), CLI values are appended to file values rather than replacing them.

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Suppressing False Positives

Some clones are intentional—boilerplate required by a language or framework. Use --suppress to silence them.

--suppress PATTERN accepts fnmatch glob patterns matched against raw source lines (including one line of context above each clone chunk, to catch decorators). If any line in either side of a clone pair matches, the group is suppressed.

You can also annotate specific sites inline—the filter reads raw source, so comments are visible even though the tokenizer strips them. Add a suppression comment to any line inside or immediately above a clone:

Language	Inline annotation
Python	# cpitd: suppress
C/C++	// cpitd: suppress
Rust	// cpitd: suppress

Then pass --suppress "*cpitd: suppress*" (or set it in pyproject.toml).

Python

Abstract base class implementations — ABCs force you to repeat method signatures across subclasses. Suppress them with:

cpitd src/ --suppress "*@abstractmethod*"

Or in pyproject.toml:

[tool.cpitd]
suppress = ["*@abstractmethod*", "*@override*"]

Protocol / interface boilerplate — if you use a decorator to mark protocol implementations (e.g. @protocol_impl), pass that pattern:

cpitd src/ --suppress "*@protocol_impl*"

C / C++

Header guards — every .h file has them. Suppress both styles:

cpitd src/ \
  --suppress "*#ifndef *_H*" \
  --suppress "*#pragma once*"

Or in pyproject.toml:

[tool.cpitd]
suppress = ["*#ifndef *_H*", "*#pragma once*"]
ignore = ["**/*.h"]   # alternatively, just skip headers entirely

Rust

Trait implementations — implementing the same trait for multiple types produces near-identical impl blocks. Suppress by matching the impl ... for ... line:

cpitd src/ --suppress "*impl * for *"

Derive macros — #[derive(Debug, Clone, PartialEq)] lines repeat everywhere but are rarely meaningful clones. Suppress them:

cpitd src/ --suppress "*#[derive(*"

In pyproject.toml:

[tool.cpitd]
suppress = [
    "*impl*Display*for*",
    "*impl*From*for*",
    "*#[derive(*",
]

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Pre-commit Hook

Add cpitd to .pre-commit-config.yaml as a local hook (cpitd must be installed in the environment where hooks run):

repos:
  - repo: local
    hooks:
      - id: cpitd-clone-detection
        name: cpitd (clone detection)
        entry: cpitd src/ --ignore "tests/fixtures/*"
        language: system
        pass_filenames: false
        always_run: true

Then install the hook:

pre-commit install

The hook runs cpitd on every commit. Tune entry with --suppress or any other flag -- or lean on [tool.cpitd] in pyproject.toml so the hook entry stays short.

To run the hook manually without committing:

pre-commit run cpitd-clone-detection

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CLI Options Reference

Flag	Default	Description
--format human|json	human	Output format
--ignore PATTERN	—	Glob patterns to exclude (repeatable)
--languages LANG	—	Restrict to specific languages (repeatable)
--suppress PATTERN	—	Suppress clones whose source lines match (repeatable)