Python Control Flow

Control Flow in Python

Control flow is the order in which individual statements, instructions, or function calls are executed. Python provides several structures for controlling program flow:

1. If Statements (Selection)

If statements allow you to execute different code based on conditions:

# Basic if statement
x = 10
if x > 5:
    print("x is greater than 5")

# if-else statement
age = 18
if age >= 18:
    print("You are an adult")
else:
    print("You are a minor")

# if-elif-else statement
score = 85
if score >= 90:
    print("A grade")
elif score >= 80:
    print("B grade")
elif score >= 70:
    print("C grade")
elif score >= 60:
    print("D grade")
else:
    print("Failed")

2. For Loops

For loops are used to iterate over sequences:

# Looping through a range
for i in range(5):
    print(i)  # Prints 0, 1, 2, 3, 4

# Looping through a list
fruits = ["apple", "banana", "orange"]
for fruit in fruits:
    print(fruit)

# Enumerate for index and value
for index, fruit in enumerate(fruits):
    print(f"{index}: {fruit}")

# Nested loops
for i in range(3):
    for j in range(2):
        print(f"i={i}, j={j}")

3. While Loops

While loops repeat as long as a condition is true:

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

# Break statement
while True:
    user_input = input("Enter 'quit' to exit: ")
    if user_input == "quit":
        break

# Continue statement
for i in range(5):
    if i == 2:
        continue  # Skip 2
    print(i)

4. Loop Control Statements

Python provides several ways to control loop execution:

# Break - exit the loop
for i in range(10):
    if i == 5:
        break
    print(i)

# Continue - skip to next iteration
for i in range(5):
    if i == 2:
        continue
    print(i)

# Pass - do nothing
for i in range(5):
    if i == 2:
        pass  # Placeholder
    else:
        print(i)

5. List Comprehensions

A concise way to create lists using loops:

# Traditional loop
squares = []
for x in range(5):
    squares.append(x**2)

# List comprehension
squares = [x**2 for x in range(5)]

# With condition
even_squares = [x**2 for x in range(10) if x % 2 == 0]

6. Combining Loops and Conditions

You can combine loops and conditions for more complex control flow:

# Find prime numbers
def is_prime(n):
    if n < 2:
        return False
    for i in range(2, int(n ** 0.5) + 1):
        if n % i == 0:
            return False
    return True

# Print prime numbers up to 20
for num in range(20):
    if is_prime(num):
        print(f"{num} is prime")

Conclusion

Control flow in Python allows for the execution of statements, instructions, or function calls in a specific order. This can be achieved through various structures:

• If Statements for making decisions based on conditions.
• For Loops for iterating over sequences such as ranges or lists.
• While Loops for repeating actions while a condition is true.
• Loop Control Statements like break, continue, and pass for controlling loop execution.
• List Comprehensions for creating lists in a concise way.
• Combining Loops and Conditions for more complex control flow, such as identifying prime numbers in a given range.