- 📘 Day 11
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- Defining a Function
- Declaring and Calling a Function
- Function without Parameters
- Function Returning a Value - Part 1
- Function with Parameters
- Passing Arguments with Key and Value
- Function Returning a Value - Part 2
- Function with Default Parameters
- Arbitrary Number of Arguments
- Default and Arbitrary Number of Parameters in Functions
- [Function as
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So far we have seen many built-in Python functions. In this section, we will focus on custom functions. What is a function? Before we start making functions, let us learn what a function is and why we need them?
A function is a reusable block of code or programming statements designed to perform a certain task. To define or declare a function, Python provides the def keyword. The following is the syntax for defining a function. The function block of code is executed only if the function is called or invoked.
When we make a function, we call it declaring a function. When we start using the it, we call it calling or invoking a function. Function can be declared with or without parameters.
# syntax
# Declaring a function
def function_name():
codes
codes
# Calling a function
function_name()Function can be declared without parameters.
Example:
def generate_full_name ():
first_name = 'Case'
last_name = 'Sprawl'
space = ' '
full_name = first_name + space + last_name
print(full_name)
generate_full_name () # calling a function
def add_two_numbers ():
num_one = 2
num_two = 3
total = num_one + num_two
print(total)
add_two_numbers()Function can also return values, if a function does not have a return statement, the value of the function is None. Let us rewrite the above functions using return. From now on, we get a value from a function when we call the function and print it.
def generate_full_name ():
first_name = 'Case'
last_name = 'Sprawl'
space = ' '
full_name = first_name + space + last_name
return full_name
print(generate_full_name())
def add_two_numbers ():
num_one = 2
num_two = 3
total = num_one + num_two
return total
print(add_two_numbers())In a function we can pass different data types(number, string, boolean, list, tuple, dictionary or set) as a parameter
- Single Parameter: If our function takes a parameter we should call our function with an argument
# syntax
# Declaring a function
def function_name(parameter):
codes
codes
# Calling function
print(function_name(argument))Example:
def greetings (name):
message = name + ', welcome to Python for Everyone!'
return message
print(greetings('Case'))
def add_ten(num):
ten = 10
return num + ten
print(add_ten(90))
def square_number(x):
return x * x
print(square_number(2))
def area_of_circle (r):
PI = 3.14
area = PI * r ** 2
return area
print(area_of_circle(10))
def sum_of_numbers(n):
total = 0
for i in range(n+1):
total+=i
print(total)
print(sum_of_numbers(10)) # 55
print(sum_of_numbers(100)) # 5050- Two Parameter: A function may or may not have a parameter or parameters. A function may also have two or more parameters. If our function takes parameters we should call it with arguments. Let us check a function with two parameters:
# syntax
# Declaring a function
def function_name(para1, para2):
codes
codes
# Calling function
print(function_name(arg1, arg2))Example:
def generate_full_name (first_name, last_name):
space = ' '
full_name = first_name + space + last_name
return full_name
print('Full Name: ', generate_full_name('Case','Sprawl'))
def sum_two_numbers (num_one, num_two):
sum = num_one + num_two
return sum
print('Sum of two numbers: ', sum_two_numbers(1, 9))
def calculate_age (current_year, birth_year):
age = current_year - birth_year
return age;
print('Age: ', calculate_age(2021, 1819))
def weight_of_object (mass, gravity):
weight = str(mass * gravity)+ ' N' # the value has to be changed to a string first
return weight
print('Weight of an object in Newtons: ', weight_of_object(100, 9.81))If we pass the arguments with key and value, the order of the arguments does not matter.
# syntax
# Declaring a function
def function_name(para1, para2):
codes
codes
# Calling function
print(function_name(para1 = 'John', para2 = 'Doe')) # the order of arguments does not matter hereExample:
def print_fullname(firstname, lastname):
space = ' '
full_name = firstname + space + lastname
print(full_name)
print(print_fullname(firstname = 'Case', lastname = 'Sprawl'))
def add_two_numbers (num1, num2):
total = num1 + num2
print(total)
print(add_two_numbers(num2 = 3, num1 = 2)) # Order does not matterIf we do not return a value with a function, then our function is returning None by default. To return a value with a function we use the keyword return followed by the variable we are returning. We can return any kind of data types from a function.
- Returning a string: Example:
def print_name(firstname):
return firstname
print_name('Case') # Case
def print_full_name(firstname, lastname):
space = ' '
full_name = firstname + space + lastname
return full_name
print_full_name(firstname='Case', lastname='Sprawl')- Returning a number:
Example:
def add_two_numbers (num1, num2):
total = num1 + num2
return total
print(add_two_numbers(2, 3))
def calculate_age (current_year, birth_year):
age = current_year - birth_year
return age;
print('Age: ', calculate_age(2019, 1819))- Returning a boolean: Example:
def is_even (n):
if n % 2 == 0:
print('even')
return True # return stops further execution of the function, similar to break
return False
print(is_even(10)) # True
print(is_even(7)) # False- Returning a list: Example:
def find_even_numbers(n):
evens = []
for i in range(n + 1):
if i % 2 == 0:
evens.append(i)
return evens
print(find_even_numbers(10))Sometimes we pass default values to parameters, when we invoke the function. If we do not pass arguments when calling the function, their default values will be used.
# syntax
# Declaring a function
def function_name(param = value):
codes
codes
# Calling function
function_name()
function_name(arg)Example:
def greetings (name = 'Peter'):
message = name + ', welcome to Python for Everyone!'
return message
print(greetings())
print(greetings('Case'))
def generate_full_name (first_name = 'Case', last_name = 'Sprawl'):
space = ' '
full_name = first_name + space + last_name
return full_name
print(generate_full_name())
print(generate_full_name('Moli','Smith'))
def calculate_age (birth_year,current_year = 2021):
age = current_year - birth_year
return age;
print('Age: ', calculate_age(1821))
def weight_of_object (mass, gravity = 9.81):
weight = str(mass * gravity)+ ' N' # the value has to be changed to string first
return weight
print('Weight of an object in Newtons: ', weight_of_object(100)) # 9.81 - average gravity on Earth's surface
print('Weight of an object in Newtons: ', weight_of_object(100, 1.62)) # gravity on the surface of the MoonIf we do not know the number of arguments we pass to our function, we can create a function which can take arbitrary number of arguments by adding * before the parameter name.
# syntax
# Declaring a function
def function_name(*args):
codes
codes
# Calling function
function_name(param1, param2, param3,..)Example:
def sum_all_nums(*nums):
total = 0
for num in nums:
total += num # same as total = total + num
return total
print(sum_all_nums(2, 3, 5)) # 10def generate_groups (team,*args):
print(team)
for i in args:
print(i)
print(generate_groups('Team-1','Case','Moli','Weah','Eyob'))#You can pass functions around as parameters
def square_number (n):
return n * n
def do_something(f, x):
return f(x)
print(do_something(square_number, 3)) # 27