Data types so far

We have seen two types of data already:

• Numbers:
  • 0
  • -124.5
• Strings:
  • 'hello'
  • 'I am 99 years old!'

Booleans

A really useful data type is a Boolean
It can represent two values - True or False

my_boolean = 5 > 2
print(my_boolean)

another_boolean = 3.14 < -3
print(another_boolean)

Comparisons

first_number = 12 / 3
second_number = 2 * 2
are_equal = first_number == second_number
print(are_equal)

2 <= 5  # but not 2 =< 5, order matters!

242 >= 242  # but not 242 => 2

Why is this useful?

Think of the program powering Hotels.com. A user can only get exclusive deals if they're a Silver Member...

This means we need to change the price depending on whether this condition is True or not!

What if...?

if x > 0:
    print('x is positive')

Indentation

if x > 0:
    print('x is positive')
print('a message that always gets printed')

if x > 0:
    print('x is positive')
    print('a message that gets printed only when x is positive')

If/else

if x > 0:
    print('x is positive')
else:
    print('x is negative')

The code under else gets executed when the if boolean is False.

They are mutually exclusive!

(⭐) 2a. ID check

• Create a variable called age.
• Write an if statement which checks if someone of that age is allowed to drink. They are only if they're 18 and over.
• If they are allowed - print "Can drink!".
• If they are not - print "You have to wait!"

If/elif/else

Sometimes there are more than two possibilities, so you need more than True/False or if/else.

if x > 0:
    print('x is positive')
elif x == 0:
    print('x is equal to 0')
else:
    print('x is negative')

elif is an abbreviation of “else if”

Please note that only one branch will be executed, and priority starts from the top!

(⭐⭐) 2b. GradeBot

Getting our code to do more

How would we write code to print all numbers between 10 and 0?

What about 100? Or 1000?

number = 10

while number > 0: 
    print(number)
    number = number - 1

print("Blast Off!")

While loops

number = 10

while number > 0: 
    print(number)
    #  number = number - 1

print("Blast Off!")

Exercise

# Use `and` to use multiple True conditions at once 
# You need to use the `number` variable in each boolean statement
if number > 5 and number < 10:
    print('This number is between 6 and 9')

# Use `or` to only require one True condition
if there_is_free_food or i_am_hungry:
    print('Time to eat!')