Module 3: Standard Constructs

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Learning outcomes

• use Python control flow correctly;
• write simple loops and comprehensions;
• recognize the syntax of common program blocks;
• explain how Python groups and repeats statements.

Prerequisites

Read Module 2 first. Be comfortable with function calls and list processing.

The idea in one sentence

Standard constructs are the everyday building blocks that let Python make decisions, repeat work, and build new values.

Everyday analogy

Think of a restaurant order system. It checks a condition, chooses one branch, repeats actions for every item, and sometimes builds a final list of items to serve.

Syntax

if score >= 75:
    grade = "Distinction"
elif score >= 40:
    grade = "Pass"
else:
    grade = "Fail"

squares = [x * x for x in range(1, 6) if x % 2 == 0]

Worked example

total = 0
for n in [1, 2, 3]:
    total += n

Step by step:

1. Start with total = 0.
2. Take n = 1, add it to total.
3. Take n = 2, add it to total.
4. Take n = 3, add it to total.
5. Final result is 6.

Why this matters in practice

• In college notes, these constructs show how code is structured.
• In real code, they are used for menus, validation, filtering, summarizing, and repeated processing.
• They are the basic grammar of almost every Python program.

Important concepts

if/elif/else

Use this when code must choose one path from several options.

if mark >= 75:
    result = "High"
elif mark >= 40:
    result = "Medium"
else:
    result = "Low"

for

Use this when you want to go through items one by one.

for item in [1, 2, 3]:
    print(item)

while

Use this when the loop should continue until a condition changes.

count = 3
while count > 0:
    count -= 1

Comprehension

Use this to create a new collection from existing data.

[x * x for x in range(5)]

Technical meaning

Standard constructs control the flow of execution. They determine how statements are grouped, how conditions are tested, and how repetition is expressed in a Python program.

Memory rule

• condition -> if
• repeated items -> for
• repeated test -> while
• new list from old data -> comprehension

Quick check

• Why is indentation important in Python?
• What does a list comprehension create?
• When should you use while instead of for?
• What does elif mean?

Short exam answer

Standard constructs are the basic control features of Python. if/elif/else selects between choices, for and while repeat work, and comprehensions build new collections in a compact form. They are the core tools for program flow.

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