Python Indentation, Spacing and Line Length (PEP 8)

Python Indentation: 4 Spaces per Level

Indentation is the space at the start of a line. In Python it's not only style: it decides which lines belong to an if, a loop or a function (chapter 8). PEP 8 adds the style part: use 4 spaces for each level.

Think of it like the chapters, sections and paragraphs in a book. Each level is moved in by the same amount, so you can see at a glance what belongs where.

The rules

• Every level adds 4 spaces: 4 inside a function, 8 inside an if in that function, 12 one level deeper.
• Use spaces, not tab characters. Set your editor so the Tab key types 4 spaces (most editors already do).
• Every line in one block lines up exactly.

123456789def count_passes(marks):
    passes = 0
    for mark in marks:
        if mark >= 40:
            passes += 1
    return passes


print(count_passes([35, 80, 52]))

Follow the spaces: the for is inside the function (4), the if is inside the for (8), and passes += 1 is inside the if (12). return is back at 4, so it runs after the loop is done.

Indentation errors

A line that's moved in for no reason:

123def greet(name):
    print("Hello", name)
        print("Welcome!")

A tab mixed with spaces. The third line below starts with one tab character, which looks the same on screen:

123456def greet(name):
    print("Hello", name)
	print("Welcome!")


greet("Sunny")

Every error is a clue! A TabError means "some lines use tabs, some use spaces". The fix is always the same: use 4 spaces everywhere.

Indent with 4 spaces per level, never tabs, and line up every block exactly.

Spaces Around Operators and After Commas

Whitespace means the spaces in your code. PEP 8 has a simple goal for them: put spaces where they help the eye split the line into parts, and nowhere else.

Think of it like the spaces between words in a sentence. Withoutspacesitishardtoread. With too many, it falls apart.

The rules

The last rule is the surprising one. = gets spaces when it stores a value in a variable. Inside the brackets of a call, like sep="-", or in a default value, like def greet(name="friend"):, it gets none.

1234567def greet(name="friend"):
    return "Hi " + name


first = greet()
second = greet(name="Sunny")
print(first, second, sep=" | ")

Don't line things up

123x     = 1
long_name = 2
print(x + long_name)

It looks neat, but when you add a longer name, you have to change the spaces on every line. PEP 8 says: one space before =, always.

Common beginner doubt: "Does print (total) with a space break the code?" No, Python runs it. That's what makes style hard: nothing warns you. You have to see it yourself.

One space around operators and after commas; no spaces inside brackets or around keyword =.

Blank Lines Between Functions

Blank lines split your program into parts, the way paragraphs split a story. PEP 8 has one clear rule for them: put two blank lines before and after every function that starts at the left edge.

Think of it like the space between two letters in a stack of mail. Each letter is one piece; the gap shows where the next one starts.

The rules

• Two blank lines before and after each function defined at the left edge (a top-level function).
• Inside a function, use one blank line now and then, to separate steps. Not after every line.
• No long runs of blank lines anywhere else.

123456789101112TAX_RATE = 0.18


def add_tax(price):
    return price + price * TAX_RATE


def print_bill(item, price):
    print(item, "costs", add_tax(price))


print_bill("Pen", 100)

Look at the shape: the constant, a gap, the first function, a gap, the second function, a gap, the main program. Your eye finds each function in a second.

One blank line inside a function

123456789def report(marks):
    total = sum(marks)
    average = total / len(marks)

    print("Total:", total)
    print("Average:", average)


report([60, 80])

The blank line separates "work it out" from "show it". That's a good reason for one blank line.

Common beginner doubt

"Does Python need these blank lines?" No. Blank lines never change what a program does. Delete them all and it prints the same thing. They're only for the reader, like everything else in PEP 8.

Two blank lines around every top-level function; one, sometimes, inside.

Line Length: About 79 Characters

PEP 8 says a line of code should be at most 79 characters long, and a comment line at most 72. Some teams agree on a little more, up to 99, but 79 is the standard.

Think of it like a newspaper. It prints text in narrow columns, because your eye loses its place on a very long line. Short lines also fit two files side by side on one screen, or a phone screen, with no scrolling sideways.

Break long lines inside brackets

Inside round ( ), square [ ] or curly brackets, Python lets a line continue on the next line. It waits for the closing bracket:

123456players = [
    "Sunny",
    "Rocky",
    "Lucky",
]
print(len(players))

A long calculation has no brackets of its own, so add a pair around it:

1234567891011rent = 12000
food = 6000
travel = 1500
internet = 800
monthly_total = (
    rent
    + food
    + travel
    + internet
)
print(monthly_total)

The rules

• Break the line inside brackets, after an opening bracket or after a comma.
• Indent the extra lines by 4 more spaces, so they don't look like a new statement.
• In a long calculation, start each new line with the operator, like + food. PEP 8 suggests this, because you can read down the operators like a sum on paper.
• Put the closing bracket on its own line, or at the end of the last line. Pick one way.

Avoid breaking without brackets

12total = 1 + 2
    + 3

Without brackets, a statement ends at the end of the line. Python thinks + 3 is a new line that's moved in for no reason.

Common beginner doubt: "What about a backslash \ at the end of a line?" It also works, but one invisible space after it breaks the code. PEP 8 prefers brackets.

Keep lines under 79 characters; to break one, use brackets and indent the rest.

Practice: Spacing

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1. 145.Fix the Indentation in a Python FunctionEasySolve
2. 146.Python Program to Break a Long Line of Code (PEP 8)MediumSolve