Learning Python Else if: Complete Guide for Beginners - w9school

In Python, the if-else statement is used for conditional execution of code based on a certain condition. It allows you to specify different blocks of code to be executed depending on whether a condition is true or false.

Learning Python Else if: Complete Guide for Beginners - w9school

Python If ... Else

In Python,

  • The if...else statement is used for conditional execution of code.

  • In Python, if...else is a conditional statement used for making decisions in your code.
  • It allows you to check a condition, and based on whether the condition is true or false, different blocks of code will be executed.

  • The if...else statement in Python is used to control the flow of your program based on specific conditions.

  • It allows you to execute different blocks of code depending on whether a given condition is true or false.

  • This conditional branching is essential for making decisions and handling various scenarios in your code.

  • If the condition is true, the code block under the if statement is executed; otherwise, the code block under the else statement is executed.

  • This enables your program to perform different actions based on the evaluation of a specific condition.

Usage of If...else in Python

Here are some common use cases for if...else statements in Python:

1- Simple Conditional Execution:

  • The most basic usage of if...else is to perform different actions based on a condition.
# Example 1
x = 10

if x > 5:
    print("x is greater than 5")
else:
    print("x is not greater than 5")

Now Try it Yourself

2- Multiple Conditions:

  • You can use elif (short for "else if") to add multiple conditions to your decision-making process.
# Example 2
num = 7

if num > 10:
    print("Number is greater than 10.")
elif num > 5:
    print("Number is greater than 5 but not greater than 10.")
else:
    print("Number is less than or equal to 5.")

Now Try it Yourself

3-Nested if...else:

  • You can nest if...else statements to create more complex decision trees.
# Example 3
x = 10

if x > 5:
    if x < 15:
        print("x is greater than 5 and less than 15.")
    else:
        print("x is greater than or equal to 15.")
else:
    print("x is not greater than 5.")

Now Try it Yourself

4- Input Validation:

  • You can use if...else to validate user input and respond accordingly.
# Example 4
user_input = input("Enter a number: ")

if user_input.isdigit():
    number = int(user_input)
    print("You entered a valid number:", number)
else:
    print("Invalid input. Please enter a valid number.")

Now Try it Yourself

5- Boolean Conditions:

  • Since if evaluates expressions that result in either True or False, you can use any boolean expression as the condition.
# Example 5
is_raining = True
have_umbrella = False

if is_raining and not have_umbrella:
    print("It's raining, and you don't have an umbrella. Get inside!")
elif is_raining and have_umbrella:
    print("It's raining, but you have an umbrella. You're good to go!")
else:
    print("It's not raining. Enjoy the weather!")

Now Try it Yourself

6- Handling Lists or Iterables:

  • You can use if...else statements to process elements of a list based on certain criteria.
# Example 6
numbers = [1, 5, 9, 12, 20]

even_numbers = []
odd_numbers = []

for num in numbers:
    if num % 2 == 0:
        even_numbers.append(num)
    else:
        odd_numbers.append(num)

print("Even numbers:", even_numbers)
print("Odd numbers:", odd_numbers)

Now Try it Yourself

These are just a few examples of how you can use if...else statements in Python to implement conditional logic and control the flow of your program based on different conditions. It's a fundamental construct in programming and allows you to make your code more dynamic and responsive.

Python Conditions and If statements

Python supports the usual logical conditions from mathematics:

  • Equals: a == b
  • Not Equals: a != b
  • Less than: a < b
  • Less than or equal to: a <= b
  • Greater than: a > b
  • Greater than or equal to: a >= b

These conditions can be used in several ways, most commonly in "if statements" and loops.

An "if statement" is written by using the if keyword.

Example

if statement:

a = 33
b = 200
if b > a:
  print("b is greater than a")‚Äč

Now Try it Yourself

Example Explained:

In this example we use two variables, a and b, which are used as part of the if statement to test whether b is greater than a. As a is 33, and b is 200, we know that 200 is greater than 33, and so we print to screen that "b is greater than a".

Indentation

Python relies on indentation (whitespace at the beginning of a line) to define scope in the code. Other programming languages often use curly-brackets for this purpose.

Example

If statement, without indentation (will raise an error):

a = 33
b = 200
if b > a:
print("b is greater than a"# you will get an error

Elif

The elif keyword is Python's way of saying "if the previous conditions were not true, then try this condition".

Example

a = 33
b = 33
if b > a:
  print("b is greater than a")
elif a == b:
  print("a and b are equal")

Now Try it Yourself

In this example a is equal to b, so the first condition is not true, but the elif condition is true, so we print to screen that "a and b are equal".

Else

The else keyword catches anything which isn't caught by the preceding conditions.

Example

a = 200
b = 33
if b > a:
  print("b is greater than a")
elif a == b:
  print("a and b are equal")
else:
  print("a is greater than b")

In this example a is greater than b, so the first condition is not true, also the elif condition is not true, so we go to the else condition and print to screen that "a is greater than b".

You can also have an else without the elif:

Example

a = 200
b = 33
if b > a:
  print("b is greater than a")
else:
  print("b is not greater than a")

Now Try it Yourself

Short Hand If

If you have only one statement to execute, you can put it on the same line as the if statement.

Example

One line if statement:

if a > b: print("a is greater than b")

Short Hand If ... Else

If you have only one statement to execute, one for if, and one for else, you can put it all on the same line:

Example

One line if else statement:

a = 2
b = 330
print("A") if a > b else print("B")

This technique is known as Ternary Operators, or Conditional Expressions.

You can also have multiple else statements on the same line:

Example

One line if else statement, with 3 conditions:

a = 330
b = 330
print("A") if a > b else print("=") if a == b else print("B")

Now Try it Yourself

And

The and keyword is a logical operator, and is used to combine conditional statements:

Example

Test if a is greater than b, AND if c is greater than a:

a = 200
b = 33
c = 500
if a > b and c > a:
  print("Both conditions are True")

Or

The or keyword is a logical operator, and is used to combine conditional statements:

Example

Test if a is greater than b, OR if a is greater than c:

a = 200
b = 33
c = 500
if a > b or a > c:
  print("At least one of the conditions is True")

Not

The not keyword is a logical operator, and is used to reverse the result of the conditional statement:

Example

Test if a is NOT greater than b:

a = 33
b = 200
if not a > b:
  print("a is NOT greater than b")

Nested If

You can have if statements inside if statements, this is called nested if statements.

Example

x = 41

if x > 10:
  print("Above ten,")
  if x > 20:
    print("and also above 20!")
  else:
    print("but not above 20.")

The pass Statement

if statements cannot be empty, but if you for some reason have an if statement with no content, put in the pass statement to avoid getting an error.

Example

a = 33
b = 200

if b > a:
  pass

Now Try it Yourself

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