Python 3

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Introduction to Python

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Introduction to User-Defined Functions

user-defined functions

A user-defined function is a block of code that can be executed by name.

def add(val1, val2):
    valsum = val1 + val2
    return valsum

ret = add(5, 10)           # int, 15

ret2 = add(0.3, 0.9)       # float, 1.2

A function is a block of code:

that can be executed by name ("calling" the function)
that may be executed with different input values
that can be executed multiple times in a program

user defined functions: calling the function

calling means activating the function and running its code.

def print_hello():
    print("Hello, World!")

print_hello()             # prints 'Hello, World!'
print_hello()             # prints 'Hello, World!'
print_hello()             # prints 'Hello, World!'

we are calling the function 3 times in this code
a function call is marked by parentheses after the function name -- this means that the function block will be run

user defined functions: arguments

The arguments are the inputs to a function.

def print_hello(greeting, person):              # note we do not
    full_greeting = f'{greeting}, {person}!'    # refer to 'name1'
    print(full_greeting)                        # 'place2', etc.
                                                # inside the function
name1 = 'Hello'
place1 = 'World'

print_hello(name1, place1)             # prints 'Hello, World!'


name2 = 'Bonjour'
place2 = 'Python'

print_hello(name2, place2)             # prints 'Bonjour, Python!'

we are calling the function, passing two arguments (inputs) to the call
the arguments are renamed in the function definition (greeting, person), and the function refers to them by these names
(the argument objects that were passed are copied to the argument names -- they are the same objects with new names)

user defined functions: function return values

A function's return value is passed back from the function using the return statement.

def print_hello(greeting, person):
    full_greeting = f'{greeting}, {person}!'
    return full_greeting

msg = print_hello('Bonjour', 'parrot')

print(msg)                                       # 'Bonjour, parrot!'

now instead of printing the greeting, we are returning it
a value is returned from the function using the return statement
the value returned is assigned to the variable assigned in the call (here, it is msg)

Ex. 9.1 - 9.5

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