Refactoring

Refactoring is the disciplined practice of changing the internal structure of code, such as renaming, splitting a long function or removing duplication, without altering its externally visible behavior.

Why it matters

Code is read far more often than it is written. Regular refactoring keeps a codebase understandable and pays down technical debt, which makes later features cheaper to add. It is only safe when tests confirm that behavior stayed the same.

Example

Before:

def total(items):
    t = 0
    for i in items:
        t = t + i["price"] * i["qty"]
    return t

After:

def line_total(item):
    return item["price"] * item["qty"]

def total(items):
    return sum(line_total(i) for i in items)

The result is the same, but each piece now has a clear name and can be tested separately.

Common mistakes

• Refactoring without tests, then discovering behavior changed.
• Mixing a refactor with a new feature in one commit, which makes review and rollback hard.
• Rewriting everything from scratch when small, incremental steps would do.

Related

• Technical debt
• Unit test
• Code review
• Function

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