Comments

A comment is a note in your code that Python ignores when running — it's there for humans. In Python, anything after a # on a line is a comment.

# This calculates a 20% tip
bill = 50
tip = bill * 0.2
print(tip)  # prints the tip amount

Comments are useful for explaining why something is done a certain way — especially when it's not obvious from the code itself. Avoid comments that just restate what the code already says clearly.

# Good: explains a non-obvious reason
retries = 3  # API is flaky, so we allow a few retries

# Not useful: just repeats the code
retries = 3  # set retries to 3

PEP 8 — Python's style guide

PEP 8 is Python's official style guide. It's not enforced by the interpreter — code that breaks it still runs — but following it makes your code far easier for other people (and future you) to read. A few of the most common conventions:

• Use snake_case for variable and function names (total_score, not TotalScore).
• Use 4 spaces per indentation level (never tabs).
• Put spaces around operators: x = 1 + 2, not x=1+2.
• Keep lines under about 79–99 characters where reasonable.
• Use blank lines to separate logical sections of code.

# Following PEP 8
first_name = "Ada"
last_name = "Lovelace"
full_name = first_name + " " + last_name
print(full_name)

You don't need to memorize the whole guide today — just build the habit of writing clean, consistently-spaced code from the start. It becomes automatic quickly.

Try it yourself

Add a comment explaining what this code does, then run it.

Checkpoint

• # starts a comment; Python ignores everything after it on that line.
• Good comments explain why, not what.
• PEP 8 is Python's style guide — snake_case, 4-space indents, spaced-out operators.