3.2 Programming Constructs in Python

This note covers advanced programming constructs in Python as required by the FBISE Grade 12 curriculum, including data structures (lists), file handling (disk I/O), and an introduction to using databases in Python.

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1. Fundamental Programming Constructs

All Python programs are built from three fundamental constructs:

1.1 Sequence

The default mode — Python executes each line one after another.

name = "Ali"
age = 17
print(name, "is", age, "years old")

1.2 Selection (if / elif / else)

Python uses indentation (4 spaces) to define code blocks — no curly braces needed.

marks = 75

if marks >= 80:
    print("A Grade")
elif marks >= 60:
    print("B Grade")
else:
    print("C Grade")

1.3 Iteration

for loop — collection-controlled; iterates over a sequence:

for i in range(1, 6):   # prints 1 to 5
    print(i)

while loop — condition-controlled; repeats while a condition is True:

count = 0
while count < 5:
    print(count)
    count += 1

Loop control statements:

• break — exits the loop entirely
• continue — skips the current iteration and moves to the next
• pass — does nothing (placeholder)

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2. Data Structures — Lists

A list is a mutable, ordered collection that can store mixed data types.

students = ["Ali", "Sara", "Ahmed"]
scores   = [85, 92, 78]

Common List Operations

Iterating Over a List

for name in students:
    print(name)

List Comprehension (Advanced)

squares = [x**2 for x in range(1, 6)]
# Result: [1, 4, 9, 16, 25]

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3. File Handling (Disk I/O)

File handling allows a program to persist data to storage (hard disk) so it survives after the program ends.

File Opening Modes

Writing to a File

with open('students.txt', 'w') as f:
    f.write("Ali\n")
    f.write("Sara\n")

Reading from a File

# Read entire file
with open('students.txt', 'r') as f:
    content = f.read()
    print(content)

# Read line by line
with open('students.txt', 'r') as f:
    for line in f:
        print(line.strip())

Appending to a File

with open('students.txt', 'a') as f:
    f.write("Ahmed\n")

Worked Example — Save a List to File

scores = [85, 92, 78, 90]

with open('scores.txt', 'w') as f:
    for score in scores:
        f.write(str(score) + '\n')

print("Scores saved successfully.")

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4. Databases in Python

Python can interact with databases using the built-in sqlite3 module (no installation needed).

Basic SQLite Workflow

import sqlite3

# 1. Connect (creates DB file if not exists)
conn = sqlite3.connect('school.db')

# 2. Create a cursor
cursor = conn.cursor()

# 3. Create a table
cursor.execute('''
    CREATE TABLE IF NOT EXISTS students (
        id   INTEGER PRIMARY KEY,
        name TEXT,
        marks INTEGER
    )
''')

# 4. Insert data
cursor.execute("INSERT INTO students VALUES (1, 'Ali', 85)")

# 5. Query data
cursor.execute("SELECT * FROM students")
rows = cursor.fetchall()
for row in rows:
    print(row)

# 6. Commit and close
conn.commit()
conn.close()

Key Database Concepts

• connect() — opens/creates a database file
• cursor() — object used to execute SQL commands
• execute() — runs an SQL statement
• fetchall() — retrieves all results as a list of tuples
• commit() — saves changes permanently
• close() — closes the connection

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Summary