In Python, proper code indentation is essential. The structure of the code is determined by its indentation, which helps improve code readability and is a fundamental principle in the language.

If you do not adhere to the correct indentation rules, you might encounter errors such as “Expected an indented block” when trying to run your Python code. This tutorial will provide a detailed explanation of how to solve this error and prevent it from happening in the future.

Understanding the Expected and Indented Block Error

“Expected an indented block” error usually occurs when the Python interpreter encounters a block of code that should be indented but is not. In Python, code blocks are usually preceded by a statement or a keyword that ends with a colon (:). The following lines in the code block should be indented by 4 spaces or a single tab.

For instance, a common cause of this error is a missing indentation in a script that uses if, elif, or else statements, as well as for or while loops.

Step 1: Find the Error Source

To fix the “Expected an indented block” error, first, determine the line number where the error occurred. Python usually displays the error message with the line number where the issue was found. For instance, consider the following code:

When you run this code, Python will return an error message similar to the following one:

IndentationError: expected an indented block

In this case, the error message does not indicate the exact line number. However, since the code is short, it is easy to spot that the print() function should be indented after the for loop.

Step 2: Fix the Indentation

You can correct the code indentation by adding the appropriate number of spaces or a tab character. It is recommended to use 4 spaces for every indentation level, as stated in the PEP 8 style guide. Make sure to consistently use either spaces or tabs only for indentation during the same project. Here’s the corrected version of the previous code example:

Now, when you run this code, it should execute without any errors.

Step 3: Check for Incorrect Indentation Levels

Sometimes, the “Expected an indented block” error might appear when there are too many spaces or tabs used for indentation. Ensure that every code block has the proper indentation level, and that inner blocks are indented to an additional level.

For example, consider this piece of code:

When you run the code, Python will return the following error message:

IndentationError: expected an indented block

In this case, the issue arises because the print() function should be indented two levels (8 spaces or 2 tabs). Here’s the corrected version of the code snippet:

Now, when you run this code, it should execute without any errors.

Full Code with Output

0
1
2
3
4

0 0
0 1
0 2
1 0
1 1
1 2
2 0
2 1
2 2

Conclusion

When you encounter the “Expected an indented block” error, track it down by examining the line numbers and the code surrounding the error message. Properly manage your code’s indentation by consistently adhering to Python’s indentation rules, and your code should execute without errors. Always follow PEP 8 best practices to ensure your code is clean and easy to read.