CODE: Python Operators and Control Flow

Python operators let programs compute and reason about values through math, logic, and comparisons. Control flow turns that reasoning into behavior, choosing paths and repeating steps until a condition changes.

Operators in Python

Operators are special symbols in Python that allow you to perform actions on values and variables. They are the foundation of calculations, comparisons, and logic in programming. Understanding operators is essential for writing expressions that drive your code’s behavior.

Arithmetic Operators

Arithmetic operators are used for basic mathematical calculations.

  • Example:

python 
a = 10
b = 3
print(a + b)  # Addition → 13
print(a - b)  # Subtraction → 7
print(a * b)  # Multiplication → 30
print(a / b)  # Division → 3.333...
print(a // b) # Floor division → 3
print(a % b)  # Modulus (remainder) → 1
print(a ** b) # Exponentiation → 1000

These operators are frequently used in numerical computations.

Comparison Operators

Comparison operators compare values and return a boolean (True or False).

  • Example:

    • python 
    x = 5
y = 10
print(x == y)  # Equal → False
print(x != y)  # Not equal → True
print(x > y)   # Greater than → False
print(x < y)   # Less than → True
print(x >= 5)  # Greater or equal → True

These are widely used in conditions and loops.

⚙️ Logical Operators

Logical operators are used to combine conditions.

  • Example:

python 
is_adult = True
has_ticket = False
print(is_adult and has_ticket)  # True only if both are True → False
print(is_adult or has_ticket)   # True if at least one is True → True
print(not is_adult)             # Negation → False

Logical operators make decision-making more powerful.

Assignment Operators

Assignment operators are used to assign values to variables, often with shorthand updates.

  • Example:

python 
x = 5
x += 3  # Same as x = x + 3 → 8
x -= 2  # Same as x = x - 2 → 6
x *= 4  # Same as x = x * 4 → 24
x /= 6  # Same as x = x / 6 → 4.0

These are useful for updating variables without rewriting the whole expression.

Other Operators

Python also has some special-purpose operators.

  • Membership operators:

python 
print("a" in "apple")   # True
print("z" not in "apple")  # True

  • Identity operators:

    • python 
    a = [1, 2, 3]
b = a
print(a is b)       # True (same object in memory)
print(a is not b)   # False

These operators are often used in more advanced logic and data handling.

Conditional Statements (if, elif, else)

Programs often need to make decisions based on certain conditions. In Python, this is done using conditional statements. These allow the program to execute different blocks of code depending on whether a condition is True or False. Mastering if, elif, and else is essential for building logic-driven applications.

The `if` Statement

The if statement checks whether a condition is true. If it is, the indented block of code will execute.

  • Example:

    • python 
    age = 18
if age >= 18:
    print("You are an adult.")

  • Here, the condition age >= 18 is evaluated, and since it is True, the message is displayed.

The `else` Clause

The else clause provides an alternative block of code to run if the condition is false.

  • Example:

    • python 
    age = 15
if age >= 18:
    print("You are an adult.")
else:
    print("You are a minor.")

  • Since the condition is False, the program runs the else block.

The `elif` Statement

The elif (short for _else if_) allows checking multiple conditions in sequence.

  • Example:

    • python 
    score = 85

if score >= 90:
    print("Grade: A")
elif score >= 75:
    print("Grade: B")
elif score >= 60:
    print("Grade: C")
else:
    print("Grade: F")

  • The program checks each condition in order and executes the first block where the condition is true.

Nested Conditions

You can place if statements inside other if statements for more complex logic.

  • Example:

    • python 
    age = 20
has_id = True

if age >= 18:
    if has_id:
        print("Access granted.")
    else:
        print("ID required.")
else:
    print("Access denied.")

  • Nested conditions provide more control but should be used carefully to keep code readable.

Loops in Python (for, while)

Loops allow programs to repeat actions automatically instead of writing the same code multiple times. Python provides two main types of loops: for loops for iterating over sequences, and while loops for repeating actions as long as a condition is true. Mastering loops is essential for handling repetitive tasks efficiently.

The `for` Loop

The for loop is used to iterate over a sequence such as a list, string, or range of numbers.

  • Example:

    • python 
    fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(fruit)

  • Output:

    • shell 
    apple
banana
cherry

  • With the range() function, you can loop through numbers:

    • python 
    for i in range(5):
    print(i)

  • Output:

    • shell 
    0
1
2
3
4

The for loop is best for known ranges or sequences.

The `while` Loop

The while loop runs as long as a condition is true.

  • Example:

    • python 
    count = 0
while count < 3:
    print("Counting:", count)
    count += 1

  • Output:

    • shell 
    Counting: 0
Counting: 1
Counting: 2

The while loop is best for unknown ranges, where you keep looping until a condition changes.

Infinite Loops

A while loop can accidentally run forever if the condition never becomes false.

  • Example (⚠️ problematic):

python 
while True:
    print("This will never stop!")

  • Always ensure a condition will eventually end the loop, or use break to exit when needed.

Combining Loops with Conditions

Loops can also include condition checks inside them for more control.

  • Example:

    • python 
    for i in range(10):
    if i % 2 == 0:
        print(i, "is even")

  • This combines looping with conditional logic for smarter programs.

Loop Control (break, continue, pass)

Sometimes you need more control inside a loop—whether to stop it early, skip certain iterations, or simply leave a placeholder for future code. Python provides three special keywords—break, continue, and pass—to handle these situations.

The `break` Statement

The break statement is used to exit a loop immediately, regardless of the loop’s condition.

  • Example:

    • python 
    for num in range(10):
    if num == 5:
        break
    print(num)

  • Output:

    • shell 
    0
1
2
3
4

Here, the loop stops as soon as num reaches 5.

The `continue` Statement

The continue statement skips the rest of the code in the current loop iteration and moves on to the next one.

  • Example:

    • python 
    for num in range(5):
    if num == 2:
        continue
    print(num)

  • Output:

    • shell 
    0
1
3
4

When num == 2, the print statement is skipped, and the loop continues.

The `pass` Statement

The pass statement does nothing—it acts as a placeholder when code is required syntactically but you don’t want to write anything yet.

  • Example:

    • python 
    for num in range(3):
    if num == 1:
        pass  # Placeholder for future code
    print("Number:", num)

  • Output:

    • shell 
    Number: 0
Number: 1
Number: 2

This is often used during development to keep the code structure valid while leaving parts empty.

Practical Exercises with Flow Control

Understanding the theory of conditionals and loops is essential, but the best way to master them is through hands-on practice. Flow control exercises help you apply if, elif, else, loops, and loop-control statements (break, continue, pass) in real-world scenarios.

Exercise 1: Even or Odd Checker

Write a program that asks the user for a number and checks whether it is even or odd.

python 
num = int(input("Enter a number: "))

if num % 2 == 0:
    print("The number is even.")
else:
    print("The number is odd.")

  • This uses conditionals to make decisions based on user input.

Exercise 2: Multiplication Table

Use a loop to print the multiplication table of a number.

python 
num = int(input("Enter a number: "))

for i in range(1, 11):
    print(f"{num} x {i} = {num * i}")

  • This demonstrates for loops and iteration with a range.

Exercise 3: Password Checker

Simulate a password prompt that allows the user up to 3 attempts.

python 
correct_password = "python123"
attempts = 0

while attempts < 3:
    password = input("Enter password: ")
    if password == correct_password:
        print("Access granted.")
        break
    else:
        print("Wrong password, try again.")
        attempts += 1
else:
    print("Too many attempts. Access denied.")

  • This combines while loops, if statements, and the break statement.

Exercise 4: Skipping Values

Print numbers from 1 to 10, but skip multiples of 3.

python 
for i in range(1, 11):
    if i % 3 == 0:
        continue
    print(i)

  • This demonstrates continue to skip specific iterations.

Exercise 5: Placeholder for Future Code

Create a program that checks grades but hasn’t implemented all rules yet.

python 
grade = 85

if grade >= 90:
    print("Excellent!")
elif grade >= 75:
    pass  # To be implemented later
else:
    print("Needs improvement.")

  • This uses pass as a placeholder while keeping the program valid.