If-Else Statement – Mastering Python

Python’s if-else statement is a fundamental control flow structure that allows your program to make decisions based on conditions. It dictates which block of code executes based on whether a condition evaluates to True or False. Understanding and effectively using if-else statements is important for writing any non-trivial Python program.

The Basic `if` Statement

The simplest form involves a single condition. If the condition is true, the indented code block is executed. Otherwise, it’s skipped.

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

This code will print “x is greater than 5” because the condition x > 5 is true.

The `if-else` Statement

This extends the if statement by adding an else block. The else block executes only if the if condition is false.

y = 3
if y > 5:
  print("y is greater than 5")
else:
  print("y is not greater than 5")

Here, the output will be “y is not greater than 5” because y > 5 is false.

`elif` (Else If) for Multiple Conditions

For situations with more than two possibilities, the elif (else if) keyword provides a concise way to chain conditions.

z = 7
if z > 10:
  print("z is greater than 10")
elif z > 5:
  print("z is greater than 5 but not greater than 10")
else:
  print("z is less than or equal to 5")

This code will print “z is greater than 5 but not greater than 10”. The conditions are checked sequentially; the first true condition’s block executes, and the rest are skipped.

Nested `if-else` Statements

You can nest if-else statements within each other to handle more complex scenarios. However, excessive nesting can reduce readability; consider refactoring into functions for better clarity if your nesting becomes too deep.

age = 20
income = 30000

if age >= 18:
  if income >= 25000:
    print("Eligible for loan")
  else:
    print("Income too low for loan")
else:
  print("Too young for loan")

Conditional Expressions (Ternary Operator)

For simple if-else logic, Python offers a concise syntax called a conditional expression:

a = 10
b = 20
max_value = a if a > b else b  # max_value will be 20
print(max_value)

This single line achieves the same result as a longer if-else block. It’s particularly useful for assigning values based on conditions.

Handling Multiple Conditions with `and` and `or`

You can combine multiple conditions using the logical operators and and or. The and operator requires both conditions to be true, while the or operator requires at least one condition to be true.

temperature = 25
is_raining = True

if temperature > 20 and not is_raining:
    print("It's a beautiful day!")
elif temperature < 10 or is_raining:
    print("It's cold or rainy!")

These examples demonstrate the versatility and power of if-else statements in Python. They are essential for creating programs that can handle different situations and make informed decisions.

The Basic if Statement

The if-else Statement

elif (Else If) for Multiple Conditions

Nested if-else Statements