IndentationError: expected an indented block

Python enforces indentation as a fundamental part of its syntax. Unlike other programming languages that use curly brackets {} or keywords like begin and end to define code blocks, Python relies solely on indentation (spaces or tabs) to indicate block structure. The error IndentationError: expected an indented block occurs when Python expects an indented code block but doesn’t find one.

This guide will break down the IndentationError, why it happens, and how to fix it with detailed explanations and examples.

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1. Understanding Indentation in Python

In Python, indentation is used to define code blocks. This includes:

• Functions
• Loops
• Conditional statements (if, elif, else)
• Class definitions
• Exception handling (try, except, finally)

Basic Example of Indentation

def greet():
    print("Hello, World!")  # This line is indented correctly.

Here, the print statement is inside the function greet() and is correctly indented.

If we remove the indentation, Python will raise an IndentationError:

def greet():
print("Hello, World!")  # IndentationError: expected an indented block

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2. Common Causes of “expected an indented block” Error

2.1. Missing Indentation

One of the most common causes is forgetting to indent after a statement that requires a block.

Example:

def say_hello():
print("Hello!")  # ❌ Error: This line should be indented

Solution:
Indent the print statement properly.

def say_hello():
    print("Hello!")  # ✅ Correct: Indented properly

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2.2. Improper Indentation After Conditional Statements

Python requires an indented block after if, elif, and else.

Example with Error:

age = 18
if age >= 18:
print("You are an adult.")  # ❌ Error: Indentation is missing

Solution:

age = 18
if age >= 18:
    print("You are an adult.")  # ✅ Correct: Indented properly

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2.3. Loops Without Indented Code

Loops (for, while) require a properly indented block.

Example with Error:

for i in range(5):
print(i)  # ❌ Error: Expected an indented block

Solution:

for i in range(5):
    print(i)  # ✅ Correct: Indented properly

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2.4. Function Definition Without Indented Code

A function must contain an indented block of code.

Example with Error:

def greet():
# No indentation here
print("Hello!")  # ❌ Error: Expected an indented block

Solution:

def greet():
    print("Hello!")  # ✅ Correct: Indented properly

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2.5. Class Definitions Without Indented Code

A class requires an indented block after its definition.

Example with Error:

class Person:
pass  # ❌ Error: If no implementation, use pass or indent a method.

Solution:

class Person:
    def greet(self):
        print("Hello!")  # ✅ Correct: Indented properly

OR
If you want an empty class, use pass:

class Person:
    pass  # ✅ Correct: `pass` prevents indentation error

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3. Mixed Spaces and Tabs

Python does not allow mixing tabs and spaces for indentation. If your code has inconsistent indentation, Python raises an error.

Example:

def example():
    print("Hello")  # Uses spaces
	print("World")  # ❌ Uses a tab (will cause an error)

Solution:
Make sure to use only spaces or tabs consistently. The recommended way is to use 4 spaces per indentation level.

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4. Fixing Indentation Errors Step by Step

1. Read the error message carefully.
   • Python tells you the line number where the indentation issue exists.
2. Check for missing indentation.
   • Ensure all function definitions, loops, and conditionals have indented blocks.
3. Avoid mixing spaces and tabs.
   • Convert all indentation to spaces (most editors do this automatically).
4. Use a code editor with indentation support.
   • VS Code, PyCharm, and Sublime Text highlight indentation errors.
5. Manually re-indent the block.
   • Select all code (Ctrl + A) and press Shift + Tab to remove indentation.
   • Then, press Tab or 4 spaces to re-indent properly.

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5. Checking Indentation in Different Editors

• VS Code
  • Enable “Render Whitespace” (Ctrl + Shift + P → “Toggle Render Whitespace”) to see spaces and tabs.
  • Use Tab to convert spaces or Shift + Tab to remove indentation.
• PyCharm
  • Check indentation settings in File > Settings > Editor > Code Style > Python.
• Sublime Text
  • View Indentation Settings and convert to spaces.