check-similarity-py

name	check-similarity-py
description	Detect duplicate Python code using AST-based similarity analysis. Use when working with .py files and looking for code duplication or refactoring opportunities.
argument-hint	[path] [--threshold 0.85] [--print]
allowed-tools	Bash(similarity-py *) Bash(cargo run -p similarity-py *) Read Grep Glob
paths	**/*.py

Python Code Similarity Detection

What to do

Run similarity-py on the target project to detect duplicate functions and classes, then analyze results and propose refactoring.

If similarity-py is not installed:

cargo install similarity-py

Step 1: Run similarity analysis

similarity-py $ARGUMENTS

If no arguments given:

similarity-py . --threshold 0.85 --min-lines 5

Step 2: Analyze results

High-priority

• 100% similarity: Identical functions with renamed variables -> extract shared function
• 95-100%: Same algorithm, different names -> parameterize
• Duplicate class methods: Same logic across classes -> extract mixin or base class

Medium-priority

• 85-95%: Similar data processing with minor differences -> shared utility
• Decorated variants: Same function with different decorators -> single function with configurable decoration

Acceptable

• Short __init__ methods that set attributes
• Property getters/setters with trivial structure

Step 3: Propose refactoring

For each high-priority pair, show before/after code.

Key Options

Option	Description
--threshold <0-1>	Similarity threshold (default: 0.85)
--min-lines <n>	Skip functions shorter than n lines (default: 3)
--print	Show actual code snippets
--filter-function <name>	Filter by function name
--fail-on-duplicates	Exit code 1 if duplicates found
--experimental-overlap	Enable partial overlap detection

Common Python refactoring patterns

• Data processing functions with different field access -> generic with key parameter
• API endpoint handlers -> shared decorator or base handler
• Validation methods -> schema-based (pydantic, attrs)
• Duplicate class methods across classes -> mixin class or standalone function
• Test setup duplication -> fixtures or shared base test class