Learn Python Indentation: Absolute Beginners Tutorial

Python uses indentation — the spaces at the start of a line — to define the structure of your code. If you are coming from another language, or if this is your first language altogether, indentation is the single concept you need to understand before anything else will make sense.

In many programming languages, you use curly braces {} to mark where a block of code begins and ends. Python takes a different approach: the block is defined entirely by how far the lines are pushed in from the left margin. This is not a style suggestion — it is a rule enforced by the interpreter at runtime. Get the spacing wrong and Python raises an IndentationError before your program even starts.

What Indentation Actually Does in Python

When Python reads your source file it looks at the leading whitespace — the spaces before the first non-space character on each line — to group lines into blocks. A block is a set of statements that belong together: the body of a function, the body of a loop, the branch of an if statement. Every time you write a statement that opens a block, you end it with a colon and then indent the lines that belong to it.

The standard unit of indentation in Python is 4 spaces. This is the recommendation of PEP 8, the official Python style guide, and every widely used Python project follows it. Your editor's Tab key can be configured to insert 4 spaces automatically — and in most Python-aware editors it is set that way by default.

The following example shows a complete function. The two lines inside the function are indented by 4 spaces. The print call after the function is at zero indentation and is therefore not part of the function body.

def greet(name):
    message = "Hello, " + name   # 4 spaces — inside the function
    return message                # 4 spaces — still inside the function

print(greet("Kandi"))             # 0 spaces — outside the function

If you removed the indentation from the return line and brought it back to zero, Python would raise a SyntaxError because a return statement outside a function is invalid. If you indented it by 3 spaces instead of 4, Python would raise an IndentationError because 3 does not match the 4-space level opened by the def.

Indentation in Functions, Loops, and Conditionals

The same rule applies everywhere a block is needed. Functions, for loops, while loops, if/elif/else chains, with statements, try/except blocks, and class definitions all use the colon-then-indent pattern. The examples below show each case with the indented lines highlighted.

Conditional blocks

score = 72

if score >= 90:
    grade = "A"          # 4 spaces — the if block
elif score >= 70:
    grade = "B"          # 4 spaces — the elif block
else:
    grade = "C"          # 4 spaces — the else block

print(grade)             # 0 spaces — after all branches

For loop body

fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    upper = fruit.upper()    # 4 spaces — inside the loop
    print(upper)             # 4 spaces — still inside the loop

print("Done.")               # 0 spaces — the loop has ended

Nested Indentation and Visual Structure

Nesting happens when one block is placed inside another — for example, an if statement inside a for loop, or a loop inside a function. Each level of nesting adds another 4 spaces. The result is a visual staircase that lets you read the program structure at a glance.

def check_scores(scores):           # 0 spaces — top level
    for score in scores:            # 4 spaces — inside function
        if score >= 90:             # 8 spaces — inside the loop
            print("Excellent")      # 12 spaces — inside the if
        elif score >= 70:           # 8 spaces — same level as if
            print("Pass")           # 12 spaces — inside elif
        else:                       # 8 spaces — same level as if
            print("Needs work")     # 12 spaces — inside else

check_scores([95, 73, 55])          # 0 spaces — back at top level

Notice how the elif and else keywords line up exactly with the if that started the chain. They are not inside the if block — they are continuations of the same conditional statement, so they sit at the same 8-space level. Only the code inside each branch is pushed in by another 4 spaces.

"Code is read more often than it is written." — Guido van Rossum, creator of Python

Python Indentation Summary Points

1. Indentation is not optional in Python — it is the syntax that defines block structure. Every block-opening statement ends with a colon, and every line inside the block is indented by a consistent number of spaces.
2. PEP 8 specifies 4 spaces per indentation level. This is the universal convention across the Python ecosystem. Never use tab characters; configure your editor to expand Tab into 4 spaces.
3. Nesting adds another 4 spaces at each level. The visual staircase this creates mirrors the logical nesting of your program. A block ends the moment a line returns to the previous indentation level — there is no closing keyword or brace.
4. An IndentationError means a line's leading whitespace does not match any open indentation level. Read the error message, find the mismatched line, and correct its spacing to match the level it belongs to.

Indentation is one of those things that feels unfamiliar for a day or two and then becomes invisible. Once your editor is configured correctly and you have written a few dozen functions and loops, you will no longer think about it consciously — the structure just looks right when it is right and wrong when it is not.