Conditions in Python — if, elif, else and Nested Conditions

Programs need to make decisions: if the marks are 90 or more, print Grade A. That's what if does.

1. if, elif, else

marks = 72

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

Grade B

• Python checks the conditions top to bottom and runs the first block whose condition is True.
• elif and else are optional. You can have many elifs.
• Every block ends with a colon : and is indented.

Order matters. If you check marks >= 60 first, a student with 95 gets "Grade B" because that condition is also true.

2. Combining conditions

age = 22
cgpa = 7.8
backlogs = 0

if age <= 25 and cgpa >= 7 and backlogs == 0:
    print("Eligible for the drive")
else:
    print("Not eligible")

Eligible for the drive

Python also allows chained comparisons: if 18 <= age <= 25: reads just like maths.

3. Nested conditions

An if inside another if:

n = -8

if n >= 0:
    print("Non-negative")
else:
    if n % 2 == 0:
        print("Negative even")
    else:
        print("Negative odd")

Negative even

Prefer elif or and when they make the code flatter and easier to read.

4. The conditional expression (one-line if)

n = 7
result = "even" if n % 2 == 0 else "odd"
print(result)

odd

5. Checking membership and empty values

city = "Jaipur"
if city in ["Jaipur", "Udaipur", "Jodhpur"]:
    print("Rajasthan")

name = ""
if not name:
    print("Name is empty")

Rajasthan
Name is empty

6. match-case (Python 3.10+)

For many fixed values, match is cleaner than a long elif chain:

day = 6
match day:
    case 6 | 7:
        print("Weekend")
    case 1 | 2 | 3 | 4 | 5:
        print("Weekday")
    case _:
        print("Invalid day")

Weekend

case _ is the default (like else).

Example: leap year

year = 2024
if (year % 4 == 0 and year % 100 != 0) or year % 400 == 0:
    print(year, "is a leap year")
else:
    print(year, "is not a leap year")

2024 is a leap year

Common mistakes

• Writing = instead of == in a condition (SyntaxError).
• Forgetting the colon or the indentation.
• Putting the broader condition before the stricter one.

Quick recap

• if → elif → else; the first True branch runs, only one.
• Combine with and, or, not; chained comparisons like 18 <= age <= 25.
• One-line form: a if condition else b.
• in checks membership; empty values are falsy.