Control Structures in Python

Control structures allow you to control the flow of your Python program by making decisions or repeating tasks. In this lesson, we will cover conditionals, loops, and the concept of indentation in Python.

1. Python Conditionals (if, elif, else)

Conditionals allow your program to make decisions based on specific conditions.

Syntax:
Python
if condition:
    # Code block executed if condition is True
elif another_condition:
    # Code block executed if the first condition is False and this one is True
else:
    # Code block executed if all above conditions are False

Example:

Python
age = 18

if age < 18:
    print("You are a minor.")
elif age == 18:
    print("Welcome to adulthood!")
else:
    print("You are an adult.")

2. Python Loops

Loops are used to execute a block of code repeatedly as long as a condition is met.

a) for Loop

The for loop is used to iterate over a sequence (like a list, tuple, dictionary, or string).

Syntax:
Python
for variable in sequence:
    # Code block to execute

Example:

Python
fruits = ["apple", "banana", "cherry"]

for fruit in fruits:
    print(fruit)
b) while Loop

The while loop continues to execute a block of code as long as the specified condition is True.

Syntax:
Python
while condition:
    # Code block to execute

Example:

Python
count = 0

while count < 5:
    print("Count:", count)
    count += 1

3. The Concept of Indentation

Python uses indentation to define blocks of code. It replaces the use of curly braces {} in other programming languages.

Example:
Python
if True:
    print("This is part of the if block.")  # Indented
print("This is outside the if block.")     # Not indented

Incorrect indentation will raise an error:

Python
if True:
print("This will cause an error!")  # Missing indentation

4. Nested Loops and Conditionals

You can combine loops and conditionals to create more complex logic.

Example:
Python
numbers = [1, 2, 3, 4, 5]

for number in numbers:
    if number % 2 == 0:
        print(f"{number} is even.")
    else:
        print(f"{number} is odd.")

5. The break, continue, and pass Statements

These statements are used to alter the normal flow of a loop:

  • break: Terminates the loop prematurely.
Python
for num in range(5):
    if num == 3:
        break
    print(num)  # Output: 0, 1, 2

continue: Skips the current iteration and moves to the next.

Python
for num in range(5):
    if num == 3:
        continue
    print(num)  # Output: 0, 1, 2, 4

pass: Does nothing; acts as a placeholder.

Python
for num in range(5):
    if num == 3:
        pass  # Placeholder
    print(num)

6. Using the range() Function

The range() function generates a sequence of numbers. It is commonly used with for loops.

Syntax:
Python
range(start, stop, step)

Example:

Python
for i in range(1, 10, 2):  # Start from 1, end at 9, step by 2
    print(i)  # Output: 1, 3, 5, 7, 9

Conclusion

In this lesson, we explored Python’s control structures, including conditionals and loops, which allow you to control the flow of your program. Mastering these concepts will enable you to write dynamic and efficient code. Up next, we’ll dive into functions, where you’ll learn how to encapsulate logic and reuse it across your programs.

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