Python- Day 15-IF Statements- Core Principles

Overview of Conditional Statements in Python:

Programming often involves examining conditions and deciding which action to take based on those conditions.

Python if statement: Enables examining the current state of a program and responding appropriately to that state.

Goal: Learn to write conditional tests that allow checking conditions of interest. You’ll write simple and complex if statements to identify exact conditions.

You’ll use these concepts with lists, allowing you to write loops that handle most items uniformly but treat certain items with specific conditions differently.

Simple Example of if Statement:

You have a list of car names, most of which should be printed in title case except for ‘bmw’, which should be printed in uppercase.

cars = ['audi', 'bmw', 'subaru', 'toyota']
for car in cars:
    if car == 'bmw':
        print(car.upper())
    else:
        print(car.title())

>>

Audi
BMW
Subaru
Toyota

The loop checks if the current value of car is 'bmw' and prints it in uppercase if true; otherwise, it prints the car name in title case.

Conditional Tests:

An expression evaluated as either True or False.

Python uses the outcome of these tests to determine whether to execute the following code block.

If the test evaluates to True, Python executes the code following the if statement.

If the test evaluates to False, Python ignores the code following the if statement.

Checking for Equality:

Equality Operator (==): Checks if the value of a variable matches a specific value.

car = 'bmw'
car == 'bmw'  # True

If the values match, the result is True; otherwise, it is False

 car = 'bmw'
 car == 'bmw'
True

 car = 'audi'
 car == 'bmw'
False

Ignoring Case When Checking for Equality:

Case Sensitivity: Python checks for case differences during comparisons.

car = 'Audi'
car == 'audi'  # False

Solution: Convert the string to lowercase using .lower() to perform case-insensitive comparisons.

car = 'Audi'
car.lower() == 'audi'  # True

Checking for Inequality:

Inequality Operator (!=): Used to check if two values are not equal.

requested_topping = 'mushrooms'
if requested_topping != 'anchovies':
    print("Hold the anchovies!")

This condition checks if the topping is not ‘anchovies’ and prints a message if true.

Numerical Comparisons:

Python allows various comparisons with numbers, such as ==, !=, <, <=, >, >=.

age = 18
age == 18  # True
age < 21   # True

Checking Multiple Conditions:

and Operator: Both conditions must be true for the overall expression to be True

age_0 = 22
age_1 = 18
age_0 >= 21 and age_1 >= 21  # False

or Operator: Only one condition needs to be true for the overall expression to be True

age_0 = 22
age_1 = 18
age_0 >= 21 or age_1 >= 21  # True

Checking Whether a Value is in a List:

in Keyword: Checks if a value exists in a list.

requested_toppings = ['mushrooms', 'onions', 'pineapple']
'mushrooms' in requested_toppings  # True
'pepperoni' in requested_toppings  # False

Checking Whether a Value is Not in a List:

not in Keyword: Used to check if a value is absent from a list.

banned_users = ['andrew', 'carolina', 'david']
user = 'marie'
if user not in banned_users:
    print(f"{user.title()}, you can post a response if you wish.")

Boolean Expressions:

A Boolean expression is a conditional test that evaluates to True or False.

Boolean values (True, False) are used to track the state of conditions in programs, such as game status or user permissions

game_active = True
can_edit = False

This structured approach covers the core principles of Python’s if statements, conditional tests, equality/inequality checks, and Boolean logic.

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