Indentation Error in Python: Solving One of the Most Common Syntax Errors!

An indentation error in Python happens when the code’s spacing or alignment is inconsistent. Python uses indentation, not braces, to define code blocks. So even a single misplaced space or tab can break execution and raise an IndentationError. This makes it one of the most common syntax issues for beginners and experienced developers alike. 

In this guide, you'll read more about what causes indentation errors, common examples with explanations, and step-by-step methods to fix them. You'll also explore the difference between indentation and tab errors, best practices to prevent them, and useful tools that help maintain consistent indentation in Python code. 

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What is an Indentation Error in Python and Why Does It Occur? 

Let’s start by understanding the error first in brief. 

• An indentation error in Python is a syntax error that occurs when your code’s indentation is inconsistent or incorrect. 
• In Python, indentation isn’t optional — it’s how the interpreter groups statements. 
• It defines: 

1. Which lines belong inside a loop 
2. Which are part of an if statement 
3. Which belong to a function or class 

When Python expects a specific level of indentation but doesn’t find it—or finds something unexpected; it raises an IndentationError. 

Why It Happens in Python (and Not in Other Languages) 

• Languages like Java, C++, or JavaScript use curly braces {} to define code blocks. 
• In those languages, indentation affects readability but not execution. 
• Python, on the other hand, uses indentation itself as a structural rule. 
• This was a deliberate design choice by Guido van Rossum to ensure clean, consistent, and readable code. 
• Since code is read more often than it’s written, enforcing indentation helps keep it clear for everyone. 

There are two main types of this error you'll encounter: 

• IndentationError: expected an indented block: This error occurs when Python expects a block of code to be indented, but it isn't. This almost always happens after a statement that ends with a colon (:), such as if, for, def, or class. 
• IndentationError: unexpected indent: This is the opposite scenario. It happens when a line of code is indented for no reason. Python sees the extra spaces and doesn't know which block this line belongs to, leading to an indentation error in python. 

Let's look at a very simple example to see it in action. 

Correct Code: 

Python 
# This code runs perfectly. 
# The print statement is correctly indented inside the if block. 
user_age = 20 
if user_age > 18: 
   print("You are eligible to vote.")  
 

Incorrect Code (Causing expected an indented block): 

Python 
# This code will fail. 
# The print statement is not indented after the if statement's colon. 
user_age = 20 
if user_age > 18: 
print("You are eligible to vote.") # This line will cause the error 
 
The traceback for the incorrect code would look like this: 
File "test.py", line 4 
   print("You are eligible to vote.") 
   ^ 
IndentationError: expected an indented block 
 

Understanding what is an indentation error in python is the first step. It’s not a bug in your logic; it's a problem with your code's structure. By mastering this concept, you embrace the "Pythonic" way of writing clean and organized code. Fixing an indentation error in python is a rite of passage for every developer. 

Common Causes of an Indentation Error in Python 

Every Python developer, from beginner to expert, has faced an indentation error in python. While they can be frustrating, the good news is that they almost always stem from a few common, easily fixable mistakes. Understanding these root causes will help you spot and correct them quickly. Let's break down the most frequent culprits. 

1. Missing Indentation After a Block Statement 

This is the most straightforward cause. As we've discussed, any line that starts a new code block ends with a colon (:). This includes if, elif, else, for, while, def, class, and try/except blocks. The line or lines of code immediately following the colon must be indented. Forgetting to do so results in an expected an indented block error. 

• Wrong: 

Python 
def say_hello(): 
print("Hello, World!") # Missing indent 
 

• Right: 

Python 
def say_hello(): 
   print("Hello, World!") # Correctly indented 
 

2. Unexpected or Incorrect Indentation 

This happens when you indent a line that doesn't belong to any preceding block. Python sees the indentation and expects it to be part of a block, but since there's no if, for, etc., to associate it with, it raises an unexpected indent error. This often occurs when a line that should be at the base level of the script is accidentally indented. 

• Wrong: 

Python 
name = "Alice" 
   print(name) # Unexpected indent 
 

• Right: 

Python 
name = "Alice" 
print(name) # Correctly aligned at the base level 
 

3. Mixing Tabs and Spaces (The Invisible Enemy) 

This is by far the trickiest indentation error in python to debug because it's visually deceptive. To you, a tab character might look identical to 4 (or 8) spaces. To the Python interpreter, they are completely different. If you indent one line with a tab and the next line with four spaces, your code might look perfectly aligned in your editor, but Python will see it as two different indentation levels and raise a TabError: inconsistent use of tabs and spaces in indentation. 

The golden rule is simple: Choose one and stick to it. The official Python style guide, PEP 8, strongly recommends using 4 spaces for indentation. 

• Wrong (Visually Aligned, Syntactically Incorrect): 

Python 
if True: 
<tab>print("This is a tab.") 
   print("This is four spaces.") # This will cause a TabError 
 

• Right (Consistent Spaces): 

Python 
if True: 
   print("This is four spaces.") 
   print("This is also four spaces.") 
 

This issue is so common that most modern code editors have settings to automatically convert tabs to spaces to help you avoid this specific indentation error in python. 

Also Read: Nested For Loop in Python: How It Works with Examples 

4. Inconsistent Indentation Levels Within the Same Block 

All lines within a single code block must be indented by the same amount. You cannot use four spaces for the first line and then two spaces for the second. This would break the logical grouping and result in an unindent does not match any outer indentation level error. 

• Wrong: 

Python 
def my_function(): 
   print("First line with 4 spaces.") 
 print("Second line with 2 spaces.") # Inconsistent indentation 
 

• Right: 

Python 
def my_function(): 
   print("First line with 4 spaces.") 
   print("Second line with 4 spaces.") 
 

To help summarize, here is a table of common causes for an indentation error in python: 

By being aware of these common pitfalls, you can quickly diagnose the root cause of nearly every indentation error in python you encounter. 

Also Read: Top 50 Python Project Ideas with Source Code in 2025 

A Step-by-Step Guide to Finding and Fixing Indentation Errors 

When you're faced with an indentation error in python, the key is to have a systematic approach to find and fix it. Don't just randomly add or remove spaces. Follow these steps to debug the issue efficiently. 

Step 1: Read the Traceback Message Carefully 

The error message, or "traceback," is your best friend. It gives you three crucial pieces of information: 

1. The file name where the error occurred. 
2. The line number where Python detected the problem. 
3. The type of error (expected an indented block, unexpected indent, etc.). 

Here's an example traceback: 

File "/Users/user/project/main.py", line 12 
   print("Processing data...") 
   ^ 
IndentationError: unexpected indent 
 

This tells you the exact file (main.py) and line number (12) to investigate.  

Also Read: How to Run a Python Project: Step-by-Step Guide, Methods & Best Practices (2025) 

Important Note: Sometimes the actual mistake is on the line before the one flagged by the interpreter. If line 12 has an unexpected indent, it could be because line 11 was a for loop that you forgot to indent code under. 

Step 2: Make Whitespace Visible in Your Code Editor 

The most notorious indentation error in python is caused by mixing tabs and spaces. To make this problem visible, configure your code editor to show whitespace characters. This will typically represent spaces as dots and tabs as arrows, instantly revealing any inconsistencies. 

Here’s how to enable it in popular editors: 

• Visual Studio Code: Go to Settings (Ctrl/Cmd + ,), search for "Render Whitespace," and set it to "all". 
• PyCharm: Go to Settings/Preferences > Editor > General > Appearance and check the box for "Show whitespaces." 
• Sublime Text: Go to Preferences > Settings and add the line "draw_white_space": "all" to your user settings. 

Once enabled, you can easily spot if a block of code is indented with a mix of tabs and spaces, which is a common reason for an indentation error in python. 

Also Read: Top 6 Python IDEs of 2025 That Will Change Your Workflow! 

Step 3: Use Your Editor's Built-in Tools 

Modern code editors are packed with features to help you avoid and fix these errors. 

• Linters: Tools like Pylint and Flake8 analyze your code as you type. They will underline or flag indentation issues in real-time, often before you even run the script. Integrating a linter into your workflow is a proactive way to catch an indentation error in python. 
• Auto-Formatters: Tools like Black, autopep8, or Ruff are game-changers. With a single command or key-press, they automatically reformat your entire file to comply with a consistent style guide (like PEP 8). Running a formatter will instantly fix almost all indentation issues, including mixed tabs/spaces and inconsistent levels. 

Step 4: Manually Inspect and Correct the Code Block 

If you prefer a manual approach, use the information from the traceback to zoom in on the problem area. 

1. Navigate to the line number indicated in the error message. 
2. Check the line above it. Does it end in a colon (:)? If so, the flagged line (and any subsequent lines in the block) must be indented. 
3. Check the alignment of the current line. Does it match the indentation of the lines above it in the same block? 
4. Look for extra indentation. Is this line indented when it shouldn't be? It should only be indented if it's part of a control structure (like an if statement or for loop). 

The "Select and Re-indent" Technique 

This is a quick and highly effective manual fix for an inconsistent block: 

1. Highlight the entire block of code that is causing the indentation error in python. 
2. Press Shift + Tab repeatedly until the entire block is un-indented and aligned at the base margin. 
3. With the block still highlighted, press Tab the required number of times to indent it correctly as a single unit. 

This process ensures that every line in the block receives the exact same indentation, eliminating any inconsistencies from mixed spaces/tabs or incorrect levels. By following these steps, you can turn a frustrating indentation error in python into a quick and simple fix. 

Also Read: Identity Operator in Python: is vs == Explained with Examples 

Best Practices to Avoid the Indentation Error in Python 

Fixing an indentation error in python is a valuable skill, but avoiding it in the first place is even better. By adopting a few key habits and configuring your tools correctly, you can significantly reduce how often you encounter this error. Here are the most effective best practices to write clean, error-free Python code from the start. 

1. Configure Your Code Editor Properly (The Golden Rule) 

This is the single most important step you can take. A well-configured editor acts as your first line of defense. Make these settings your default for all Python projects: 

• Use Spaces, Not Tabs: Set your editor to insert spaces when you press the Tab key. This is the cornerstone of avoiding the infamous mixed tabs and spaces issue. 
• Set Tab Size to 4 Spaces: The universally accepted standard in the Python community (as per the PEP 8 style guide) is to use 4 spaces per indentation level. This ensures your code is readable and consistent with what other developers expect. 
• Enable "Trim Trailing Whitespace": Configure your editor to automatically remove any extra spaces at the end of lines when you save a file. While not always a cause of an indentation error in python, this practice promotes cleaner code. 
• Make Whitespace Visible: As mentioned in the debugging section, always have visible whitespace characters turned on. It helps you build an intuitive understanding of your code's structure. 

Setting this up once means you'll rarely have to think about a potential indentation error in python caused by your editor's behavior again. 

2. Adopt a Code Formatter and Linter 

Don't rely solely on your own eyes to catch every mistake. Automate the process of maintaining clean code. 

• Code Formatter (e.g., Black, Ruff): A formatter is a tool that automatically rewrites your code to conform to a specific style guide. Black, known as "The Uncompromising Code Formatter," is particularly popular because it offers very few configuration options. You run it on your code, and it handles all formatting, including indentation, for you. Integrating this into your workflow (e.g., having it run every time you save a file) eliminates indentation as a source of concern. 
• Linter (e.g., Pylint, Flake8): A linter is a static code analysis tool that flags programming errors, bugs, and stylistic issues. It will alert you to an indentation error in python in real-time, often by underlining the problematic code directly in your editor, allowing you to fix it before you even run the program. 

3. Be Consistent and Follow PEP 8 

Consistency is key. The Python community has a shared style guide called PEP 8, which provides a set of recommendations for writing readable Python code. Adhering to its guidelines, especially the rule of using 4 spaces for indentation, means your code will be easy for you and others to read. It also drastically reduces the chance of an indentation error in python because you are following a single, clear standard. 

4. Write and Run Code in Small Increments 

When you're writing a new function or a complex loop, avoid writing hundreds of lines of code before testing it. Instead, write a small, logical chunk, like a single for loop or an if-else block, and then run your script. If you encounter an indentation error in python, you'll know it's in the few lines you just wrote, making it incredibly easy to find and fix. This iterative approach is far more efficient than trying to debug a massive block of new code. 

By integrating these practices into your daily coding habits, the indentation error in python will become a rare inconvenience rather than a common frustration. 

Also Read: Python Cheat Sheet: From Fundamentals to Advanced Concepts for 2025 

How can upGrad help you in Mastering Indentation in Python? 

Indentation errors are one of the most common challenges when learning Python, but the good news is they’re easy to avoid with the right approach. The key to solving it is understanding Python’s strict whitespace rules and following best practices consistently. 

upGrad’s comprehensive courses can help you master these skills, making your coding smoother and more efficient.These courses are ideal for developers seeking to enhance their coding skills and avoid common coding errors. 

In addition to the primary programs covered in the blog, here are some additional free courses to complement your learning journey:

• Core Java Basics
• Java Object-oriented Programming
• JavaScript Basics from Scratch
• Advanced JavaScript for All

If you're unsure where to begin or which area to focus on, upGrad’s expert career counselors can guide you based on your goals. You can also visit a nearby upGrad offline center to explore course options, get hands-on experience, and speak directly with mentors!

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