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In Python, if tests (also known as conditional statements) allow you to make decisions in your code. They help the program decide which action to take based on whether a condition is true or false.

The basic format of an if test is:

if condition:
    # action if the condition is true

Components of an If Statement:

  1. Condition: A test (like checking if a number is greater than 10).
  2. Action: The code that runs if the condition is true.

Step-by-Step Explanation

1. Simple If Test

Let’s start with a simple example:

age = 18

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

Explanation:

  • age = 18: We are checking if the person is 18 years or older.
  • if age >= 18: This checks whether the age is greater than or equal to 18.
  • print("You are an adult."): If the condition is true (the person is 18 or older), it will print “You are an adult.”

Sample Output:

You are an adult.

2. Else Statement: Running Code if Condition is False

An else statement is used to run code when the condition is false. Here’s how you can use it:

age = 16

if age >= 18:
    print("You are an adult.")
else:
    print("You are not an adult yet.")

Explanation:

  • If the person is not 18 or older (i.e., if the condition is false), the code under else will run.

Sample Output:

You are not an adult yet.

3. Elif Statement: Checking Multiple Conditions

Sometimes, you might want to check more than two conditions. You can use elif (which stands for “else if”) to check additional conditions:

age = 20

if age >= 65:
    print("You are a senior citizen.")
elif age >= 18:
    print("You are an adult.")
else:
    print("You are a minor.")

Explanation:

  • The program checks if the person is a senior citizen (65+).
  • If the person is not a senior, it checks if they are an adult (18+).
  • If neither condition is true, it prints that the person is a minor.

Sample Output:

You are an adult.

4. Nested If Statements

You can also put one if statement inside another to check more complex conditions. This is called a nested if statement.

age = 25
income = 5000

if age >= 18:
    if income >= 3000:
        print("You are an adult and have a good income.")
    else:
        print("You are an adult, but your income is low.")
else:
    print("You are a minor.")

Explanation:

  • First, the program checks if the person is 18 or older.
  • Then, inside that check, it checks if the person’s income is greater than or equal to 3000.

Sample Output:

You are an adult and have a good income.

5. Using Logical Operators (and, or, not)

Sometimes, you want to check multiple conditions at once. This is where logical operators like and, or, and not come into play.

  • and: Returns True if both conditions are true.
  • or: Returns True if at least one condition is true.
  • not: Reverses the result of the condition (True becomes False, and False becomes True).

Here’s an example using and and or:

age = 20
has_permission = True

if age >= 18 and has_permission:
    print("You are allowed to enter.")
else:
    print("You are not allowed to enter.")

Explanation:

  • The person must be at least 18 years old and have permission.
  • The code will only print “You are allowed to enter” if both conditions are true.

Sample Output:

You are allowed to enter.

Now, let’s use or:

age = 16
has_permission = True

if age >= 18 or has_permission:
    print("You are allowed to enter.")
else:
    print("You are not allowed to enter.")

Explanation:

  • The person can enter if they are 18 or older, or if they have permission.

Sample Output:

You are allowed to enter.

6. Using the not Operator

You can use not to reverse a condition:

age = 15

if not age >= 18:
    print("You are not an adult yet.")
else:
    print("You are an adult.")

Explanation:

  • This checks if age is not greater than or equal to 18 and prints the corresponding message.

Sample Output:

You are not an adult yet.
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