What is IndentationError: Unexpected Indent?

The IndentationError: unexpected indent is raised when Python encounters an incorrectly indented line of code. Unlike many programming languages, Python relies on indentation to define code blocks, making consistent indentation critical.

Common Scenarios and Solutions

1. Mixing Tabs and Spaces

Using both tabs and spaces in the same block of code:

// Incorrect
def greet():
    print('Hello')  # Indented with spaces
	print('World')   # Indented with a tab

Solution: Use a consistent indentation style (spaces are recommended):

// Correct
def greet():
    print('Hello')
    print('World')

2. Extra Indentation

Adding unnecessary indentation outside of a block:

// Incorrect
print('Hello')
    print('World')  # Unexpected indent

Solution: Ensure lines are aligned correctly:

// Correct
print('Hello')
print('World')

3. Missing Indentation in Blocks

Failing to indent code after a statement that requires a block:

// Incorrect
if True:
print('Hello')

Solution: Indent the code block properly:

// Correct
if True:
    print('Hello')

4. Incorrect Indentation Level

Using inconsistent indentation levels within the same block:

// Incorrect
for i in range(3):
    print(i)
       print(i * 2)  # Incorrect level of indentation

Solution: Ensure all lines in the block are at the same level:

// Correct
for i in range(3):
    print(i)
    print(i * 2)

5. Copy-Pasting Code

Copying code from external sources with inconsistent or hidden characters:

// Incorrect
for i in range(3):
  print(i)  # Contains invisible characters

Solution: Reformat the code in your editor to ensure proper indentation:

// Correct
for i in range(3):
    print(i)

Debugging IndentationError

• Enable Editor Whitespace Visibility: Configure your editor to display tabs and spaces to identify issues easily.
• Use a Linter: Tools like Flake8 or Pylint can catch and highlight indentation problems.
• Reformat Code: Most modern editors provide auto-formatting features to fix inconsistent indentation.
• Manually Align Code: Use a consistent number of spaces (e.g., 4 spaces per level).

Best Practices to Avoid IndentationError

• Stick to spaces instead of tabs for indentation and configure your editor accordingly.
• Set your editor to automatically replace tabs with spaces (most Python developers use 4 spaces).
• Enable a PEP 8 linter to enforce Python's style guide for consistent formatting.
• Test small code snippets in an interactive Python shell to catch indentation issues early.
• Use a version control system like Git to track formatting changes.

Conclusion

The IndentationError: unexpected indent is a common but easily preventable issue in Python development. By adhering to best practices and using modern tools, you can write clean, error-free Python code with consistent indentation.

FAQs

1. What causes IndentationError: unexpected indent in Python?

This error occurs when Python encounters improperly indented code, such as mixing tabs and spaces or adding unnecessary indentation.

2. How can I fix this error?

Ensure consistent indentation using spaces (not tabs) and align all lines within a block at the same level.

3. What tools can help prevent this error?

Linters like Flake8, editors with PEP 8 support, and auto-formatting tools can help avoid indentation errors.

4. Can copy-pasting code cause this error?

Yes, copying code from external sources may introduce hidden characters or inconsistent formatting.

5. How many spaces should I use for indentation in Python?

The Python style guide (PEP 8) recommends using 4 spaces per indentation level.