Comments: Notes for Humans

What is a comment?

A comment is a note you write inside your code for people to read. Python completely ignores it. A comment starts with the # symbol.

# This program greets the user
print("Welcome!")  # this part is also a comment

Output

Welcome!

Only Welcome! is printed. Everything after # on a line is skipped.

Why write comments?

• To explain why you did something.
• To remind yourself what the code does when you come back weeks later.
• To help teammates understand your work.

Turning code off

You can put # in front of a line of code to switch it off for a moment without deleting it:

print("This line runs")
# print("This line does not run")

Output

This line runs

Tip: Good comments explain the why. You don't need a comment like # print hello above print("hello") – the code already says that.