IndentationError: expected an indented block

You ran your file and Python stopped before it did anything:

  File "shelf.py", line 2
    print("Hi")
    ^
IndentationError: expected an indented block after function definition on line 1

  File "shelf.py", line 2
    print("Hi")
    ^
IndentationError: expected an indented block after function definition on line 1

Nothing ran. Not one line. That feels like a bigger failure than it is.

What Python is actually saying

Most languages use curly brackets to show which lines belong together. Python uses space. The indent isn’t decoration — it’s how Python knows where a block starts and stops.

So when you write this:

def greet():
print("Hi")

def greet():
print("Hi")

Python reads: here comes a function, and… nothing. The next line is back at the left margin, so it’s outside the function. A function with nothing in it isn’t allowed, so Python stops and tells you the block it expected never arrived.

The fix

Indent the line that belongs inside:

def greet():
    print("Hi")

def greet():
    print("Hi")

Four spaces. That’s it.

The other version of this error

The same error appears with a different message when the indentation is inconsistent:

IndentationError: unexpected indent

IndentationError: unexpected indent

That one means a line is indented when nothing above it opened a block:

name = "Maya"
    print(name)      # indented for no reason

name = "Maya"
    print(name)      # indented for no reason

Nothing on line 1 opens a block, so line 2’s indent has nowhere to belong.

The cause almost nobody mentions

Tabs and spaces look identical on screen and are different characters underneath. Copy a snippet from Stack Overflow that used tabs, paste it into a file that uses spaces, and your code looks perfectly aligned while Python sees two different things.

Fix it once, permanently: in VS Code, click Spaces in the bottom bar, set it to 4, then run Convert Indentation to Spaces. You will never think about it again.

What to check, in order

1. Does every line after a : sit further right than the line above it?
2. Is every level exactly four spaces?
3. Did you paste this code from somewhere else?

Remember this

A colon opens a block. The indent is what fills it. Consistent four-space indentation, every file, no exceptions.

This is one of thirty errors covered in the Python Troubleshooting Handbook — each with the broken code, the fix, and why the fix works.

Next: SyntaxError: invalid syntax