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Indentation blocks

Learn Python's indentation-based block structure.

What is indentation?

In Python indentation shows which block a line of code belongs to. While other languages use curly braces { }, Python uses whitespace.

Lines after an if or for line are inside that block when they are indented. The standard indent is four spaces.

if True:
    print("Yes")
    print("Still inside the block")

If indentation is inconsistent Python raises an IndentationError. So follow the indent size your team uses.

Inconsistent indent error

Lines in the same block must be indented the same amount. If one line has a different number of spaces, Python raises an error.

if True:
    print("A")
      print("B")  # 6 spaces — error

Do not mix tabs and spaces. Make your editor convert tabs to spaces. PEP 8 recommends four spaces.

Practice Write the if block

Write a block starting with if True:. Inside the block, print Indent works with print. Indent with four spaces.

Starter code

main.py
if True:

Sample solution

main.py
if True:
    print("Indent works")

Expected output

Indent works

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 What defines blocks in Python?

  • Curly braces
  • Parentheses
  • Semicolons
  • Indentation Correct answer

Explanation: Python uses indentation to define blocks.

2 Complete the block

Question 
if True:
    ____("Yes")
Answer 
if True:
    print("Yes")

Explanation: print is inside the if block.

3 Match each concept

Term Meaning
Indent Block definition
Four spaces PEP 8 standard
Tab Do not mix with spaces
IndentationError Inconsistent indent

All lessons in Beginner

1 Python basics

  1. What is Python?
  2. REPL and print
  3. Comments
  4. Indentation blocks
  5. python -c and scripts
  6. Summary - Python basics

2 Variables

  1. Variable assignment
  2. Multiple assignment
  3. Naming variables
  4. id and type
  5. Swapping variables
  6. Summary - Variables

3 Data types

  1. int and float
  2. bool
  3. str basics
  4. None
  5. Type conversion
  6. Summary - Data types

4 Project: Calculator

  1. Project design
  2. Add/subtract
  3. Multiply/divide
  4. Error handling
  5. Putting it together

5 Operators

  1. Arithmetic
  2. Comparison
  3. Logical
  4. Bitwise
  5. Membership and identity
  6. Summary - Operators

6 String basics

  1. f-string
  2. Concatenation
  3. str.format
  4. Raw strings
  5. Triple-quote
  6. Summary - String basics

7 Conditionals

  1. The if statement
  2. elif and else
  3. Nested if
  4. Truthiness
  5. Conditional expression
  6. Summary - Conditionals

8 Loops

  1. The for loop
  2. range
  3. The while loop
  4. break and continue
  5. Loop else
  6. Summary - Loops

9 Project: Shopping cart

  1. Cart design
  2. Adding items
  3. Calculating totals
  4. Updating quantity
  5. Putting it together

10 Lists

  1. Declaring lists
  2. Index and slice
  3. List methods
  4. in and count
  5. Sorting lists
  6. Summary - Lists

11 List comprehension

  1. Comprehension basics
  2. Filtered comprehension
  3. Dict and set comprehension
  4. Nested comprehension
  5. Generator expression
  6. Summary - List comprehension

12 Tuple, set and dict

  1. Tuple
  2. Set
  3. Dict basics
  4. Dict methods
  5. Dict comprehension
  6. Summary - Tuple, set and dict

13 Functions

  1. def
  2. return
  3. Docstring
  4. Default parameters
  5. *args and **kwargs
  6. Summary - Functions

14 Function parameters

  1. Positional parameters
  2. Keyword parameters
  3. Keyword-only
  4. Positional-only
  5. Type hints basics
  6. Summary - Function parameters

15 Project: To-do CLI

  1. Task model
  2. Adding tasks
  3. Listing tasks
  4. Completing tasks
  5. Putting it together

16 Advanced string methods

  1. split and join
  2. strip, lstrip, rstrip
  3. replace
  4. find and index
  5. startswith, endswith
  6. Summary - Advanced strings

17 Input and output

  1. input()
  2. int/float conversion
  3. print parameters
  4. f-string formatting
  5. sys.argv
  6. Summary - Input and output

18 Error handling

  1. try/except
  2. else and finally
  3. raise
  4. Exception hierarchy
  5. Custom exceptions
  6. Summary - Error handling

19 Modules

  1. import
  2. from import
  3. as alias
  4. __name__ == '__main__'
  5. Standard library
  6. Summary - Modules

20 Beginner final

  1. Project design
  2. Data model
  3. Business logic
  4. Error handling
  5. Putting it together