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Conditionals

Conditionals#

  • if

  • elif

  • else

Conditionals are statements that check for a condition, using the if statement, and then only execute a set of code if the condition evaluates as True. 
value = 5

if value == True:
    print('if statement executed')
elif value == False:
    print('elif statement executed')
else: 
    print('else statement executed')

Conditionals#

Any expression that can be evaluated as a boolean, such as value comparisons, can be used with conditionals. 
speed_limit = 65
speed = 60

if speed > speed_limit:
    ticket = True
elif speed == speed_limit:
    ticket = 'warning'
else:
    ticket = False

print(ticket)

False

Properties of conditionals#

  • All conditionals start with an if, can have an optional and variable number of elif’s and an optional else statement

  • Conditionals can take any expression that can be evaluated as True or False.

  • At most one component (if / elif / else) of a conditional will run

  • The order of conditional blocks is always if then elif(s) then else

  • Code following if/elif is only ever executed if the condition is met

Activity: Conditionals I#

Complete the question in this Google Form (https://forms.gle/h7LZNmD4WcpveLam6) and then click submit.

# SPACE TO TEST THINGS OUT

Functions + Conditionals#

Let’s define a more interesting function than what we did in the functions lecture. Here we are using conditionals within our function.

# Determine if a value is even or odd
def even_odd(value): 

    if value % 2 == 0: 
        out = "even"
    else: 
        out = "odd"
        
    return out

# Execute our function to check that
# it is working according to our expectations
even_odd(6)

Code Style: Conditionals#

  • avoid single line statements

  • a single conditional (if + elif + else) has no additional line spaces between statements

Conditionals: Good Code Style#

value = 16

if value % 2 == 0:
    out = "even"
else:
    out = "odd"

Conditionals: Code Style to Avoid#

if value%2==0:out="even" # avoid statement on same line as conditional
                         # avoid blank line between if and else
else:out="odd"           # don't forget about spacing around operators!

Activity: Conditionals II#

Complete the question in this Google Form (https://forms.gle/ebekT5weU4mgwsNq9) and then click submit.

There are three questions, the third of which requires coding:

In a previous lecture, we wrote a function convert_to_f…but you’d probably want a function that could go in both directions.

Write a function convert_temperature that will convert a temperature C->F and F->C, returning the converted temperature.

Note: A temperature in Celsius will be multiplied by 9/5 and then 32 will be added to that quantity to convert to Fahrenheit. A temperature in Fahrenheit would have 32 subtracted and then that quantity multiplied by 5/9.

## SPACE TO TEST THINGS OUT

Activity: Collections#

Activity: Conditionals III#

Commplete the question in this Google Form (https://forms.gle/n45ykyKZa5RwMoCSA) and then click submit

Write a function called calculate_tip that uses the bill_amount and tip_percent, will return the tip and the total amount to pay

Now for the catch: we want it to calculate the tip correctly whether people enter a proportion (i.e. .2 to represent 20%) or a percent (i.e. 20 to represent 20%)…we’re going to assume that a value greater than zero but less than or equal to 1 is a proportion.

Test cases: calculate_tip(100, .10) and calculate_tip(100, 10) should both return the tip of 10.0 and a total of 110.0

Final note: two variables can be returned from a function if they are separated by a comma

## SPACE TO TEST THINGS OUT

## NOTE TO SELF: discuss keyword vs. positional arguments

Summary#

  • if/elif/else

  • Code Style

  • Conditionals + Functions

Collections (sneak peak)#

  • ability to store more than one piece of information in a single variable

  • lists, dictionaries, tuples

# list
my_list = [1, 2, 3, 4,]

# tuple
my_tuple = (1, 2, 3, 4)

# dictionary
my_dictionary = {'Shannon': 'mom',
                 'Josh': 'dad',
                 'Kayden': 'kid'}

Indexing#

  • access a value or set of values from of a collection

  • uses square brackets []

my_list[0]

Lists are mutable; tuples are not#

my_list[0] = 6
my_list

# THIS WILL ERROR
my_tuple[0] = 6
my_tuple
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