Functions

Functions are the same as they were in math. They take some input and return some output.

There are two types of functions:

• "Pure" functions: they take input and then return output, they have no side effects
• "Impure" functions: they can take input, but also change the variables passed to input

Lets look at function syntax in python:

# we use the `def` keyword to specify and create functions
def add(x,y):
    print("x is {} and y is {}".format(x, y)) # .format is another way of doing f-strings
    return x + y  # Return values with a return statement

print(add(5,6)) # note that this both runs the function and prints its result

lets break down each part of the statement:

• def tells python that we want to create a new function
• add is the name of this function we are creating
• x and y are arguments in this function
  • arguments are things the function can take as input and work with. They are their own variables that get passed from whatever calls the function
• return tells python to stop executing code, and instead return the following value to whatever called the function

when we do add(5, 6) python will take 5 and assign it to x and then 6 and assign it to y

# we can also call functions with keyword arguments
def add(x, y):
    print("x is {} and y is {}".format(x, y))
    return x + y  

result = add(y=6, x=5) # keyword arguments can arrive in any order
print(result)

functions can also include no arguments

def say_hi():
	print("Hi!")

say_hi()

Returning multiple values (with tuple assignments)

def swap(x, y):
    return y, x  # Return multiple values as a tuple without the parenthesis.
                 # (Note: parenthesis have been excluded but can be included)

x = 1
y = 2
x, y = swap(x, y)     # => x = 2, y = 1
# (x, y) = swap(x,y)  # Again the use of parenthesis is optional.
print(x,y)

After this, try out Challenge 5

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