Mastering Python Conditional Statements

Mastering Python Conditional Statements: if, if-else, if-elif-else & More

Python’s conditional statements help in decision-making by executing code blocks based on specified conditions. Understanding if, if-else, and if-elif-else statements is crucial for writing logical and efficient programs. Let’s explore them with practical examples.

1. The if Statement

The if statement evaluates a condition, and if it holds True, the corresponding block of code executes.

if True:
    print("Statement is true")

if False:
    print("Statement is false")  # This will not execute

Example:

x = 20
if x > 10:
    print("X is greater than 10")

x = 20
if x < 10:
    print("X is less than 10")  # No output, as the condition is False

Checking Membership in Lists:

L = [10, 20, 30, 40, 50]
if 20 in L:
    print("20 is a member of L")

2. The if-else Statement

The if-else structure helps define an alternative action if the condition is False.

x = 20
if x > 10:
    print("X is greater than 10")
else:
    print("X is less than 10")

Example: Checking Even or Odd Numbers

values = {}
x = int(input("Enter a value: "))
if x % 2 == 0:
    values[str(x)] = "Even"
else:
    values[str(x)] = "Odd"

print(values)

3. The if-elif-else Statement

When multiple conditions need evaluation, the if-elif-else structure is useful.

mark = 75
if mark >= 80:
    Grade = "A"
elif mark >= 65:
    Grade = "B"
elif mark >= 50:
    Grade = "C"
else:
    Grade = "Repeat"

print(Grade)

Using Logical Operators in Conditions

Python supports logical operators (and, or, not) to create complex conditions.

Example: Using and

x = 30
if x > 10 and x < 50:
    print("X is in the correct region")
else:
    print("X is out of the region")

Example: Using or

x = 30
if x > 10 or x == 50:
    print("X is in the correct region")
else:
    print("X is out of the region")

Example: Using not

x = 30
if not x > 10 or x == 50:
    print("X is in the correct region")
else:
    print("X is out of the region")

5. Implementing Login Authentication with if-else

details = {"Sam": "ABC", "Kane": "XYZ", "Jane": "PQR"}
username = input("Please enter your username: ")
if username in details:
    password = input("Please enter your password: ")
    if password == details[username]:
        print("You have logged in successfully!!!")
    else:
        print("Check your password...")
else:
    print("You are not in the system. Please check your username again.")

6. Inline Decision Making (Ternary Operator)

Python provides a concise way to write simple if-else conditions in a single line.

Example:

x = 20
y = 10
if x > 10: y = 30
print(y)  # Output: 30

Using a Ternary Operator:

fruit = 'Apple'
check_apple = "Yes" if fruit == 'Apple' else "No"
print(check_apple)  # Output: Yes

Assigning Grades Conditionally:

mark = 90
grade = "A" if mark >= 80 else "B" if mark >= 65 else "C" if mark >= 50 else "F"
print(grade)  # Output: A