4.16 Coding Standards (PEP 8)

PEP 8 is Python’s official style guide. This section covers it from the syntax angle — the specific formatting rules that affect how code is laid out on the page.

Indentation

4 spaces per indentation level; never mix tabs and spaces (mixing raises a TabError in Python 3).

Line Length

Limit lines to 79 characters (or up to 99 by some team conventions) — keeps code readable side-by-side in diffs and split editor panes.

Naming

snake_case for variables/functions, PascalCase for classes, UPPER_SNAKE_CASE for constants — the same table introduced in Introduction to Python.

Imports

One import per line, grouped in order: standard library, then third-party packages, then local application imports — with a blank line between each group.

import os
import sys

import boto3

from myapp.utils import helper

Whitespace

Use a single space around operators and after commas; avoid extra spaces right inside brackets or right before a function call’s parentheses.

# PEP 8 compliant
total = price * quantity
func(a, b, c)

# Not PEP 8 compliant
total = price*quantity
func( a,b,c )

Quick Interview Answer

“PEP 8 is Python’s official style guide — 4-space indentation, a 79-character line limit, snake_case/PascalCase/UPPER_SNAKE_CASE naming by identifier type, imports grouped stdlib → third-party → local with one per line, and consistent spacing around operators. Tools like black or flake8 enforce most of it automatically, so it’s rarely a manual judgment call on a real team.”

Common Mistakes

• Mixing import groups together instead of ordering standard library, then third-party, then local application imports.
• Inconsistent spacing around operators (price*quantity vs price * quantity) that a formatter like black would catch automatically.
• Treating PEP 8 as optional style preference rather than the shared convention that keeps a team’s codebase consistently readable.