IndentationError: Expected an indented block Fix
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IndentationError: Expected an indented block Fix 2026
Unlike other languages that use
{} to define blocks of code, Python uses whitespace (indentation). An IndentationError is Python's way of saying: 'I don't know where this block starts or ends.'1. The Proof Code (The Crash)
def greet_user():
# ❌ CRASH: IndentationError: expected an indented block
print("Hello!")2. The 2026 Execution Breakdown
- Syntax Definition: In Python, structures like
def,if,for, andwhilemust be followed by an indented block of code. - The Scanner: During the parsing phase, Python's scanner tracks the 'indentation level'. If the level doesn't increase after a colon
:, it stops execution. - Conclusion: Correct indentation is not just a style choice; it is part of the language's grammar.
3. The Modern Fix
Ensure every block (following a
:) is consistently indented. The 2026 industry standard is 4 Spaces per level. Avoid using Tabs, as they can represent different widths on different machines.def greet_user():
# ✅ SUCCESS: Correctly indented with 4 spaces
print("Hello!")4. Senior Secret: 'Tab/Space Mixed' Ghost Bugs
One of the most frustrating Python bugs is when a file looks correct but crashes with an
IndentationError. This happens when some lines use 4 spaces and others use 1 Tab. To fix this in 2026, use the 'Convert Indentation to Spaces' command in VS Code or enable 'Render Whitespace' to see the invisible characters.5. Troubleshooting Checklist
- Missing Colon: Did you forget the
:at the end of theifordefline? - Inconsistent Spacing: Did you use 2 spaces on one line and 4 on the next?
- Empty Blocks: Python doesn't allow empty blocks. Use the
passkeyword if you have a block with no code yet.
Top Interview Questions
?Interview Question
Q:Why does Python use indentation instead of braces?
A:
Python uses indentation to enforce 'The Zen of Python': Code should be readable and clean. By making indentation part of the grammar, Python ensures that all code follows a consistent, horizontal structure.
?Interview Question
Q:How do I fix the 'mixed tabs and spaces' error?
A:
Most modern IDEs (like VS Code) have a button in the status bar that says 'Spaces: 4'. Click it and select 'Convert Indentation to Spaces' to standardize the entire file.
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