Python Code Style Guide for Students (PEP 8 Simplified)

Why Code Style Matters

Readable code is easier to debug, grade, and maintain. Examiners don't explicitly award style marks, but clean code is easier to follow — meaning more partial credit when something goes wrong.

Rule 1: Naming

Variables and Functions: lowercase_with_underscores

# Good
student_name = "Chan"
def calculate_total(items):
    ...

# Bad
StudentName = "Chan"
def calcTotal(items):   # camelCase is for Java/JS

Constants: UPPER_CASE

MAX_STUDENTS = 40
PI = 3.14159

Classes: CapitalizedWords

class StudentRecord:
    ...
class BankAccount:
    ...

Rule 2: Indentation

Use 4 spaces. Never tabs. Be consistent.

if x > 0:
    print("positive")   # 4 spaces
    if x > 100:
        print("large")   # 8 spaces

Rule 3: Spaces Around Operators

# Good
x = 5 + 3
if y == 10:
a, b = 1, 2

# Bad
x=5+3
if y==10:
a ,b=1 ,2

Rule 4: Blank Lines

• 2 blank lines between functions
• 1 blank line between logical sections in a function

def function_one():
    pass


def function_two():
    pass

Rule 5: Line Length

Keep lines under 80 characters. If longer, break them:

# Too long
result = some_function_with_long_name(argument_one, argument_two, argument_three)

# Better
result = some_function_with_long_name(
    argument_one,
    argument_two,
    argument_three
)

Rule 6: Imports

# At top of file, one per line
import math
import random
from datetime import datetime

# Not this:
import math, random

Rule 7: Comments

Explain why, not what:

# Bad: describes what code says
total += 1  # increment total

# Good: explains reasoning
# Skip header row in CSV
next(reader)

Rule 8: Docstrings (Optional)

def calculate_grade(score):
    """Return letter grade from numeric score."""
    if score >= 80: return 'A'
    ...

Rule 9: Avoid Magic Numbers

# Bad
if score >= 50:
    print("pass")

# Better
PASS_MARK = 50
if score >= PASS_MARK:
    print("pass")

Rule 10: Meaningful Names

# Bad
x = 40
y = []
for a in x:
    y.append(a * 2)

# Good
num_students = 40
doubled = []
for n in range(num_students):
    doubled.append(n * 2)

Quick Checklist for HKDSE

• ☑ 4-space indentation (consistent)
• ☑ Meaningful variable names
• ☑ Spaces around operators
• ☑ One statement per line
• ☑ No trailing whitespace