conditional_statements.md

In our everyday living, we perform action based on a decision, situation or condition:

Take a taxi if we are already late for work; else, we will take the jeepney.

Now let's switch to our geeky world and alas, we were in a situation where:

• We only want to execute a block of code depending on a condition:

Add points to a customer if s/he presented a reward card.

• We need to perform different actions based on the situation:

Sends out SMS if customer has enough load, else prompt for an insufficient balance message.

Python offers decision making statements in order for us to conditionally execute a block of code. But before introducing those, let us recall that an action will only be executed if it meets a condition or situation, expressions that evaluates to True or False. Let's try to code some expressions!

Conditional Expressions

!> Conditional expressions are expressions that evaluates to either True or False.

# EXPRESSIONS

# Using literal values
is_late = True
is_card_presented = False
print(is_late, is_card_presented)

# Null or Zero values evaluates to False
customer_card = None
print(customer_card)

# Using operations
customer_load = 99

customer_load == 100  # Evaluates to False
customer_load > 0  # Evaluates to True
"Nissin".startswith("c")  # Evaluates to False

Expressions? Checked! Let's dive to some Python decision making statements:

Conditional Statements

• If statements

is_card_presented = False
customer_points = 10
if is_card_presented:
        # Can you shorten the expression below?
        customer_points = customer_points + 1

• If...else statements

def send_message(message):
    # This is a function, we will learn more about this on our next session!
    print('Sending: {}'.format(message))
    
    
customer_load = 100
message = 'Happy to serve!'
if customer_load > 0:
        # call our function
        send_message(message)
        print('Your message is sent!')
        # Again, can you shorten the expression below?
        customer_load = customer_load - 1
else:
        print('You have insufficient balance.')

Takeaways

• Notice how we group the actions(block of codes) above? We use the colon : to indicate the start of an indented block of code and grouped them by whitespaces.
• PEP8 recommends using 4 whitespaces for code indentation.

Challenge

Aling Nena stores her soft drink stock on two refrigerators. She stores Coke, Sprite and Royal on her Sari-sari store's refrigerator while RC and 7UP can be found on her house's refrigerator.

Help Aling Nena to properly respond to her customer when buying softdrinks.

The reply will depend if the soft drink brand is on the store's ref, on the house's ref or none. If the customer buys a soft drink brand that is:

1. stored on the store, she will respond Got it!
2. stored on the house, she will respond Please wait for a while!
3. not sold by her, she will respond Sorry we do not sell that. We only have <input here the soft drink brands>

!> Please use below template

filename

challenge_partial

Put your thinking cap on!

• What are the different ways to write conditional statements?