Engineering Craft › Clean Code & Principles

Long Method

A function doing too much; one of the most common smells.

Also known as: long function, large function, god function

A long method is a function that has grown to do too much. It’s one of the most common code smells, because functions rarely start long. They accumulate a line here and an if there.

Signs:

• You have to scroll to see it all.
• It has sections separated by blank lines or comments like # validate, # calculate, # save.
• Its name is vague (process, handle, run), because it does many things.
• It mixes levels of detail: business rules next to string formatting and database calls.
• It’s hard to test, because every test must set up everything.

def place_order(request):
    # validate
    ...30 lines...
    # compute prices and discounts
    ...40 lines...
    # save
    ...20 lines...
    # send emails
    ...15 lines...

The fix

Extract each section into a function named for its purpose (extract function):

def place_order(request):
    order = validate(request)
    priced = apply_pricing(order)
    saved = save(priced)
    notify_customer(saved)
    return saved

Now the top-level function reads like an outline. Each piece is small, testable on its own and has a name that explains it.

Rules of thumb

• No hard line limit. Many teams aim for functions that fit on one screen, and that you can describe in one sentence (single responsibility).
• Comments that label sections are a hint to extract.
• Deep nesting often goes along with length (deep nesting).
• Don’t split mechanically. Pieces should be meaningful units, not arbitrary slices with ten parameters each.
• Refactor with tests passing (refactoring).