PEP 8 (Python Enhancement Proposal 8) is the style guide for writing Python code. It helps you write code that is clean, readable, and consistent with the wider Python community.

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✅ PEP 8

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📏 1. Indentation

• Use 4 spaces per indentation level.

def my_function():
    x = 1
    if x > 0:
        print("Positive")

🔴 Avoid tabs or mixing tabs and spaces.

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📚 2. Maximum Line Length

• Keep lines ≤ 79 characters (for code)
• Keep comments/docstrings ≤ 72 characters

# This is a comment that is short and sweet

For long expressions:

# OK - Implicit line continuation inside parentheses
total = (first_variable
         + second_variable
         + third_variable)

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🧾 3. Blank Lines

• Top-level functions/classes: 2 blank lines
• Methods inside a class: 1 blank line

class MyClass:
    
    def method_one(self):
        pass

    def method_two(self):
        pass

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🔤 4. Imports

• Import standard libraries, third-party libraries, and local imports in separate sections with blank lines in between.
• Always import each module on a separate line

# Correct
import os
import sys

# Wrong
import sys, os

Ordering:

import os
import sys

import requests

import my_local_module

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🧠 5. Naming Conventions

Type	Convention	Example
Variable	lower_case_with_underscores	total_count
Function	lower_case_with_underscores	calculate_sum()
Class	CapitalizedWords	MyClass
Constants	ALL_CAPS	MAX_RETRIES
Modules	short_lowercase	utils.py
Private	_single_leading_underscore	_internal
Special	__double_underscores__	__init__

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❓ 6. Use of Whitespace

👍 Correct:

x = 1
y = 2
z = x + y

👎 Wrong:

x=1
y =2
z= x+y

More guidelines:

• No space before a comma, semicolon, colon:

  print(x, y)

• Yes space after:

  print(x, y)

• No space inside brackets:

  my_list = [1, 2, 3]

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🧾 7. Comments

Inline comments:

x = x + 1  # Increment x

Block comments:

# This function adds two numbers
# and returns the result
def add(x, y):
    return x + y

Docstrings (triple quotes):

def add(x, y):
    """Add two numbers and return the result."""
    return x + y

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✅ 8. Comparison to None and Booleans

• Use is / is not with None, not == or !=:

if x is None:
    ...

• Avoid comparisons to True or False:

# Good
if is_valid:
    ...

# Bad
if is_valid == True:
    ...

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🧼 9. Avoid Unnecessary Expressions

# Good
if not x:
    ...

# Bad
if x == False:
    ...

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🧰 10. Function and Class Definitions

Leave 2 blank lines before top-level functions and classes.

def my_function():
    ...

class MyClass:
    ...

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🧹 11. Using linters

Tools like flake8, pylint, or black automatically check or format code according to PEP 8.

black auto-formats your code:

pip install black

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🧩 12. Continuation Line Indentation

Use 4 spaces for wrapped lines, aligning naturally or with parentheses:

# Align with open delimiter
my_function(param_one, param_two,
            param_three, param_four)

# Or aligned with first argument
my_function(
    param_one, param_two,
    param_three
)

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🧮 13. Avoid Lambda for Complex Logic

# OK
squares = map(lambda x: x*x, numbers)

# Better for readability
def square(x): return x*x
squares = map(square, numbers)

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❌ 14. Don't Use Wildcard Imports

# Bad
from math import *

# Good
from math import sqrt, pi

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⚙️ 15. Consistent Exception Handling

try:
    ...
except ValueError as e:
    print(e)

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📦 16. Avoid Mutable Defaults

# Bad
def add_item(item, my_list=[]):
    my_list.append(item)
    return my_list

# Good
def add_item(item, my_list=None):
    if my_list is None:
        my_list = []
    my_list.append(item)
    return my_list

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🧑‍💻 Summary

Concept	Rule/Best Practice
Indentation	4 spaces
Line length	≤ 79 characters
Imports	Grouped: stdlib, 3rd-party, local
Naming	Use snake_case, PascalCase, UPPER_CASE
Comments	Use inline & block, write meaningful
Whitespace	Be consistent, avoid extra spaces
Docstrings	Use triple quotes for functions/classes
Tools	Use black, flake8, isort, etc.

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