python-debug

name	python-debug
description	Debug common Python runtime errors by reading tracebacks and applying targeted fixes.
version	0.1.0
source_model	claude-opus-4
extracted_from	{"total_traces":15,"passed_traces":13,"failed_traces":2,"extractor":"reflective@0.1","extracted_at":"2024-06-01T00:00:00+00:00"}
triggers	["traceback","error","exception","TypeError","AttributeError","KeyError","IndexError"]
domains	["python","debugging"]
license	Apache-2.0

When to use

Apply this skill when you encounter a Python runtime error (traceback) and need to identify the root cause and produce a minimal fix. Covers: TypeError, AttributeError, KeyError, IndexError, ImportError, ValueError, RecursionError, async misuse, off-by-one errors, and mutable default arguments.

Procedure

1. Read the traceback bottom-to-top: identify the exception type and message
2. Locate the failing line and its immediate context
3. Classify the error into one of the known patterns below
4. Apply the corresponding fix pattern
5. Verify the fix handles edge cases (None values, empty collections, boundary indices)

Fix patterns

• TypeError (concat): Use str() or f-string to convert non-string operands
• TypeError (None operation): Add a guard or provide a default return value
• AttributeError (None): Add if x is not None guard or use getattr(x, attr, default)
• AttributeError (typo): Correct the method/attribute name spelling
• KeyError: Use dict.get(key, default) instead of direct access
• IndexError (empty): Check if collection before indexing
• IndexError (off-by-one): Use len(x) - 1 or adjust range bounds
• ImportError: Correct the import name casing/spelling
• ValueError (parse): Wrap in try/except with a fallback value
• ValueError (unpack): Match the number of variables to the tuple length
• Mutable default: Use None as default, assign inside the function body
• Async (missing await): Add await before coroutine calls
• Off-by-one (range): Use range(start, end + 1) for inclusive upper bound
• RecursionError: Add a base case that returns without recursing

Examples

fix-type-error-concat

Input: result = "count: " + 42 Fix: result = "count: " + str(42)

fix-key-error-missing

Input: user['role'] when key doesn't exist Fix: user.get('role', 'unknown')

fix-mutable-default

Input: def add_item(item, lst=[]) Fix: def add_item(item, lst=None): lst = lst if lst is not None else []

Anti-patterns

• Do not catch broad Exception without re-raising or logging
• Do not use type(x) == T when isinstance(x, T) is appropriate
• Do not silence errors with empty except: pass blocks
• Do not add defensive checks everywhere — fix the root cause instead
• Do not use hasattr as a substitute for understanding the data model