Python if elif else Statement - Conditional Logic Tutorial

What are Conditional Statements?

Conditional statements let your program make decisions - executing different code based on whether a condition is True or False. Python uses if, elif, and else.

if Statement

age = 20

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

# Nothing happens if condition is False
temperature = 15
if temperature > 30:
    print("It's hot!")  # not printed

if-else Statement

if-else

score = 75

if score >= 60:
    print("Pass")
else:
    print("Fail")

# Check even or odd
number = 17
if number % 2 == 0:
    print(f"{number} is even")
else:
    print(f"{number} is odd")   # 17 is odd

if-elif-else Statement

Use elif (short for "else if") to check multiple conditions in sequence.

if-elif-else

score = 82

if score >= 90:
    grade = "A"
elif score >= 80:
    grade = "B"
elif score >= 70:
    grade = "C"
elif score >= 60:
    grade = "D"
else:
    grade = "F"

print(f"Grade: {grade}")  # Grade: B

# Multiple conditions with and/or
age = 25
income = 50000

if age >= 18 and income >= 30000:
    print("Loan approved")
elif age >= 18 or income >= 50000:
    print("Partial approval")
else:
    print("Not eligible")

Nested if Statements

Nested if

num = 15

if num > 0:
    print("Positive")
    if num % 2 == 0:
        print("and even")
    else:
        print("and odd")   # Positive and odd
elif num < 0:
    print("Negative")
else:
    print("Zero")

Ternary (Conditional) Expression

A one-line shorthand for simple if-else. Syntax: value_if_true if condition else value_if_false

Ternary Expression

age = 20
status = "adult" if age >= 18 else "minor"
print(status)  # adult

# Equivalent to:
# if age >= 18:
#     status = "adult"
# else:
#     status = "minor"

# In a print statement
x = 42
print("positive" if x > 0 else "non-positive")  # positive

# Nested ternary (use sparingly - can hurt readability)
score = 75
grade = "A" if score >= 90 else "B" if score >= 80 else "C" if score >= 70 else "F"
print(grade)  # C

match Statement (Python 3.10+)

Python's structural pattern matching - similar to switch/case in other languages but much more powerful.

match Statement

command = "quit"

match command:
    case "quit":
        print("Quitting...")
    case "help":
        print("Showing help")
    case "start":
        print("Starting...")
    case _:           # default (wildcard)
        print(f"Unknown command: {command}")

# Match with conditions (guards)
point = (0, 5)
match point:
    case (0, 0):
        print("Origin")
    case (x, 0):
        print(f"On x-axis at {x}")
    case (0, y):
        print(f"On y-axis at {y}")   # On y-axis at 5
    case (x, y):
        print(f"Point at ({x}, {y})")

Truthy and Falsy Values

In Python, conditions don't have to be explicit True/False. Many values are considered truthy or falsy.

Falsy Values	Truthy Values
`False`	`True`
`None`	Any non-zero number
`0`, `0.0`, `0j`	Non-empty string
`""` (empty string)	Non-empty list/tuple/set/dict
`[]`, `()`, `{}`, `set()`	Any object by default

Truthy/Falsy in Practice

name = ""
if name:
    print(f"Hello, {name}")
else:
    print("Name is empty")   # Name is empty

items = []
if items:
    print("Has items")
else:
    print("Empty list")      # Empty list

# Pythonic way to check for None
result = None
if result is None:
    print("No result yet")

# Pythonic way to provide defaults
username = ""
display = username or "Guest"
print(display)  # Guest