Control Structures

1. If Statements

The simplest form of control flow. It executes a block of code only if a condition is true.

Example:

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

Output:

You are an adult.

Best Practices:

• Keep conditions simple and readable.
• Use comments to explain complex conditions.

2. if-else Statements

Allows you to execute one block of code if the condition is true and another if it’s false.

Example:

age = 16
if age >= 18
    print("You are an adult.")
else:
    print("You are a minor.")

Output:

You are a minor.

3. if-elif-else Statements:

Handles multiple conditions.

Example:

age = 16
if age < 13:
    print("You are a child.")
elif age < 18:
    print("You are a teenager.")
else:
    print("You are an adult.")

Output:

You are a teenager.

Best Practices:

• Ensure all possible conditions are covered to avoid unexpected behavior.
• Use elif to make the code more readable instead of nested if-else.

4. Nested If Statements:

Nested if statements allow you to check multiple conditions by placing one if statement inside another if statement. This can be useful for handling more complex decision-making scenarios.

Example:

number = 15
if number > 10:
    if number % 2 == 0:
        print("The number is greater than 10 and even.")
    else:
        print("The number is greater than 10 and odd.")
else:
    print("The number is 10 or less.")

Output:

The number is greater than 10 and odd.

5. For Loops

Explanation: A for loop iterates over a sequence (like a list, tuple, or string) and executes a block of code for each element in the sequence.

Example:

fruits = ["apple", "banana", "cherry"]
for fruit in fruits:
    print(fruit)

Output:

apple
banana
cherry

Example:

for i in range(3):
    print("Hello, World!")

Output:

Hello, World!
Hello, World!
Hello, World!

Best Practices:

• Use meaningful variable names for loop variables.
• Avoid modifying the sequence you’re iterating over.

6. while Loops

A while loop repeats as long as a condition is true.

Example:

codecount = 1
while count <= 3:
    print(count)
    count += 1

Output:

1
2
3

Example 2:

password = ""
while password != "1234":
    password = input("Enter the password: ")
print("Access granted.")

Output (after entering “1234”):

Enter the password: 0000
Enter the password: 1234
Access granted.

Best Practices:

• Ensure the condition will eventually become false to avoid infinite loops.
• Keep the loop logic simple and clear.

7. Loop Control Statements:

Explanation:

Control the flow of loops using break and continue.

• break: Exits the loop immediately.
• continue: Skips the rest of the code inside the loop for the current iteration and moves to the next iteration.

Example with break:

for i in range(10):
    if i == 5:
        break
    print(i)

Output:

0
1
2
3
4

Example with continue:

for i in range(10):
    if i % 2 == 0:
        continue
    print(i)

Output:

0
1
2
3
4

Best Practices:

• Use break and continue sparingly for clearer and more maintainable code.
• Avoid deeply nested loops and conditions.

8. List Comprehensions

Explanation:

List comprehensions provide a concise way to create lists.

Example:

squares = [x**2 for x in range(1, 6)]
print(squares)

Output:

[1, 4, 9, 16, 25]

Example 2:

evens = [x for x in range(10) if x % 2 == 0]
print(evens)

Output:

[0, 2, 4, 6, 8]

Best Practices:

• Use list comprehensions for simple and readable code.
• Avoid overly complex comprehensions that can be hard to read.

9. Dictionary Comprehensions

Explanation:

Dictionary comprehensions create dictionaries in a concise way.

Example:

squares = {x: x**2 for x in range(1, 6)}
print(squares)

Output:

{1: 1, 2: 4, 3: 9, 4: 16, 5: 25}

Example 2:

word_lengths = {word: len(word) for word in ["Python", "is", "awesome"]}
print(word_lengths)

Output:

{'Python': 6, 'is': 2, 'awesome': 7}

Best Practices:

• Use dictionary comprehensions for concise and readable code.
• Avoid complex comprehensions that reduce readability.

10. Try-Except:

The try-except block in Python is used to handle exceptions (errors) that occur during the execution of a program. It allows the program to continue running even if an error occurs, providing a way to gracefully handle potential problems.

try:
    result = 10 / 0
except ZeroDivisionError:
    print("Cannot divide by zero.")

Output:

Cannot divide by zero.