IndentationError: expected an indented block

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Root Cause

Unlike languages that use curly braces `{}` to define code blocks, Python uses whitespace indentation. This error is a strict syntax error indicating that the Python interpreter expected an indented block of code following a control flow statement (like `if`, `for`, `while`, `def`, or `class`) ending with a colon `:`, but found code at the same or lesser indentation level. It also occurs if you mix tabs and spaces inconsistently within the same file.

Fix / Solution

Ensure that exactly one level of indentation (standard is 4 spaces) follows any statement ending in a colon. If your editor is mixing tabs and spaces, configure it to convert tabs to spaces automatically. You can use tools like `pylint` or `flake8` to catch indentation issues before running the code. If a block is intentionally empty, use the `pass` keyword.

Code Snippet

# ❌ Syntax error: print statement is not indented
def greet():
print("Hello")

# ✅ Correct indentation (4 spaces)
def greet():
    print("Hello")

# ✅ Intentionally empty block
if condition:
    pass
else:
    print("Done")