refactoring

Python Refactoring Guide

Code Smells and Their Refactorings

1. isinstance Chains → Dictionary Dispatch

Smell: Multiple isinstance checks to handle different types:

# Before - isinstance chain
for node in ast.walk(tree):
    if isinstance(node, ast.ClassDef):
        handle_class(node, defined, graph)
    elif isinstance(node, ast.FunctionDef):
        handle_function(node, defined, graph)

Refactoring: Use a dictionary mapping types to handler functions:

# After - dictionary dispatch
_node_handlers = {
    ast.ClassDef: _handle_class_def,
    ast.FunctionDef: _handle_function_def,
}

for node in ast.walk(tree):
    handler = _node_handlers.get(type(node))
    if handler:
        handler(node, defined, graph)

Benefits:

• Open for extension (add new types without modifying dispatch logic)
• Explicit mapping of types to behavior
• Unknown types handled uniformly (silently skipped or raise, your choice)

---

2. Complex Boolean Conditions → Named Helper Functions

Smell: Long boolean expression that's hard to understand:

# Before - inline complex condition
if (type(func) is ast.Attribute
    and type(func.value) is ast.Name
    and func.value.id == "self"
    and class_name is not None):
    # handle self.method() call

Refactoring: Extract to a well-named function. Use TypeGuard when the condition narrows a type:

# After - named helper with TypeGuard
from typing import TypeGuard

def _is_self_method_call(func: ast.expr, class_name: str | None) -> TypeGuard[ast.Attribute]:
    """Check if func is a self.method() call within a class."""
    return (type(func) is ast.Attribute
            and type(func.value) is ast.Name
            and func.value.id == "self"
            and class_name is not None)

# Usage - type checker knows func is ast.Attribute after this
if _is_self_method_call(func, class_name):
    qualified = f"{class_name}.{func.attr}"  # No assert needed

Benefits:

• Self-documenting code (the function name explains intent)
• TypeGuard eliminates need for asserts or casts
• Reusable across multiple call sites