Python Functions

Functions

Functions are blocks of code that does something more complex in order to avoid repeating the same logic, or most of the same logic in our code. As the program grows, function makes the program more organized.

There are mainly two types of functions.

User-define functions - The user-defined functions are those define by the user to perform the specific task.
Built-in functions - The built-in functions are those functions that are pre-defined in Python.

Creating a function

Python provides the def keyword to define the function. The syntax of the define function is given below.

The def keyword, along with the function name is used to define the function.
The identifier rule must follow the function name.
A function accepts the parameter (argument), and they can be optional.
The function block is started with the colon (:), and block statements must be at the same indentation.
The return statement is used to return the value. A function can have only one return

def my_function(parameters):
      function_block
return expression

Function Calling

In Python, after the function is created, we can call it from another function. A function must be defined before the function call; otherwise, the Python interpreter gives an error.

#function definition
def hello_world():
    print("hello world")
# function calling
hello_world()

Output:

hello world

The return statement

The return statement is used at the end of the function and returns the result of the function. It terminates the function execution and transfers the result where the function is called. The return statement cannot be used outside of the function.

Syntax:

return [expression_list]

It can contain the expression which gets evaluated and value is returned to the caller function. If the return statement has no expression or does not exist itself in the function then it returns the None object.

Example 1:

# Defining function
def sum():
    a = 10
    b = 20
    c = a+b
    return c
# calling sum() function in print statement
print("The sum is:",sum())

Output:

The sum is: 30

We have defined the function named sum, and it has a statement c = a+b, which computes the given values, and the result is returned by the return statement to the caller function.

Example 2: Creating function without return statement

# Defining function
def sum():
    a = 10
    b = 20
    c = a+b
# calling sum() function in print statement
print(sum())

Output:

None

We have defined the same function without the return statement as we can see that the sum() function returned the None object to the caller function.

Arguments in function

The arguments are types of information which can be passed into the function. The arguments are specified in the parentheses. We can pass any number of arguments, but they must be separate them with a comma.

Example 1:

#defining the function
def func (name):
    print("Hi ",name)
#calling the function
func("Devansh")

Output:

Hi Devansh

Example 2:

#Python function to calculate the sum of two variables
#defining the function
def sum (a,b):
    return a+b;

#taking values from the user
a = int(input("Enter a: "))
b = int(input("Enter b: "))

#printing the sum of a and b
print("Sum = ",sum(a,b))

Output:

Enter a: 10
Enter b: 20
Sum =  30

Call by reference in Python

In Python, call by reference means passing the actual value as an argument in the function. All the functions are called by reference, i.e., all the changes made to the reference inside the function revert back to the original value referred by the reference.

Example 1: Passing Immutable Object (List)

#defining the function
def change_list(list1):
    list1.append(20)
    list1.append(30)
    print("list inside function = ",list1)

#defining the list
list1 = [10,30,40,50]

#calling the function
change_list(list1)
print("list outside function = ",list1)

Output:

list inside function =  [10, 30, 40, 50, 20, 30]
list outside function =  [10, 30, 40, 50, 20, 30]

Example 2: Passing Mutable Object (String)

#defining the function
def change_string (str):
    str = str + " Hows you "
    print("printing the string inside function :",str)

string1 = "Hi I am there"

#calling the function
change_string(string1)

print("printing the string outside function :",string1)

Output:

printing the string inside function : Hi I am there Hows you
printing the string outside function : Hi I am there

Types of arguments

There may be several types of arguments which can be passed at the time of function call.

1. Required arguments
2. Keyword arguments
3. Default arguments
4. Variable-length arguments

Required Arguments

Till now, we have learned about function calling in Python. However, we can provide the arguments at the time of the function call. As far as the required arguments are concerned, these are the arguments which are required to be passed at the time of function calling with the exact match of their positions in the function call and function definition. If either of the arguments is not provided in the function call, or the position of the arguments is changed, the Python interpreter will show the error.

Example 1:

    def func(name):
        message = "Hi "+name
        return message
    name = input("Enter the name:")
    print(func(name))

Output:

Enter the name: John
Hi John

Example 2:

#the function simple_interest accepts three arguments and returns the simple interest accordingly
def simple_interest(p,t,r):
    return (p*t*r)/100
p = float(input("Enter the principle amount? "))
r = float(input("Enter the rate of interest? "))
t = float(input("Enter the time in years? "))
print("Simple Interest: ",simple_interest(p,r,t))

Output:

Enter the principle amount: 5000
Enter the rate of interest: 5
Enter the time in years: 3
Simple Interest:  750.0

Example 3:

#the function calculate returns the sum of two arguments a and b
def calculate(a,b):
    return a+b
calculate(10) # this causes an error as we are missing a required arguments b.

Output:

TypeError: calculate() missing 1 required positional argument: 'b'

Keyword Arguments (**kwargs)

Python allows us to call the function with the keyword arguments. This kind of function call will enable us to pass the arguments in the random order.

The name of the arguments is treated as the keywords and matched in the function calling and definition. If the same match is found, the values of the arguments are copied in the function definition.

Example 1:

#function func is called with the name and message as the keyword arguments
def func(name,message):
    print("printing the message with",name,"and ",message)

    #name and message is copied with the values John and hello respectively
    func(name = "John",message="hello")

Output:

printing the message with John and  hello

Example 2:

#The function simple_interest(p, t, r) is called with the keyword arguments the order of arguments doesn't matter in this case
def simple_interest(p,t,r):
    return (p*t*r)/100
print("Simple Interest: ",simple_interest(t=10,r=10,p=1900))

Output:

Simple Interest:  1900.0

Example 3:

#The function simple_interest(p, t, r) is called with the keyword arguments.
def simple_interest(p,t,r):
    return (p*t*r)/100

# doesn't find the exact match of the name of the arguments (keywords)
print("Simple Interest: ",simple_interest(time=10,rate=10,principle=1900))

If we provide the different name of arguments at the time of function call, an error will be thrown.

Output:

TypeError: simple_interest() got an unexpected keyword argument 'time'

Example 4:
The Python allows us to provide the mix of the required arguments and keyword arguments at the time of function call. However, the required argument must not be given after the keyword argument, i.e., once the keyword argument is encountered in the function call, the following arguments must also be the keyword arguments.

def func(name1,message,name2):    
    print("printing the message with",name1,",",message,",and",name2)    
#the first argument is not the keyword argument    
func("John",message="hello",name2="David")

Output:

printing the message with John , hello ,and David

Example 5:
The following example will cause an error due to an in-proper mix of keyword and required arguments being passed in the function call.

def func(name1,message,name2):
    print("printing the message with",name1,",",message,",and",name2)
func("John",message="hello","David")

Output:

SyntaxError: positional argument follows keyword argument

Example 6: Many arguments using Keyword argument
Python provides the facility to pass the multiple keyword arguments which can be represented as **kwargs. It is similar as the *args but it stores the argument in the dictionary format.

This type of arguments is useful when we do not know the number of arguments in advance.

def food(**kwargs):
    print(kwargs)
food(a="Apple")
food(fruits="Orange", Vagitables="Carrot")

Output:

{'a': 'Apple'}
{'fruits': 'Orange', 'Vagitables': 'Carrot'}

Default Arguments

Python allows us to initialize the arguments at the function definition. If the value of any of the arguments is not provided at the time of function call, then that argument can be initialized with the value given in the definition even if the argument is not specified at the function call.

Example 1:

def printme(name,age=22):
    print("My name is",name,"and age is",age)
printme(name = "john")

Output:

My name is John and age is 22

Example 2:

def printme(name,age=22):
    print("My name is",name,"and age is",age)
printme(name = "john") #the variable age is not passed into the function however the default value of age is considered in the function
printme(age = 10,name="David") #the value of age is overwritten here, 10 will be printed as age

Output:

My name is john and age is 22
My name is David and age is 10

Variable-length Arguments

In large projects, sometimes we may not know the number of arguments to be passed in advance. In such cases, Python provides us the flexibility to offer the comma-separated values which are internally treated as tuples at the function call. By using the variable-length arguments, we can pass any number of arguments.

However, at the function definition, we define the variable-length argument using the *args (star) as *<variable - name >.

Example 1:

def printme(*names):
    print("type of passed argument is ",type(names))
    print("printing the passed arguments...")
    for name in names:
        print(name)
printme("john","David","smith","nick")

Output:

type of passed argument is  <class 'tuple'>
printing the passed arguments...
john
David
smith
nick

In the above code, we passed *names as variable-length argument. We called the function and passed values which are treated as tuple internally. The tuple is an iterable sequence the same as the list. To print the given values, we iterated *arg names using for loop.

Functions#

Creating a function#

Function Calling#

The return statement#

Arguments in function#

Call by reference in Python#

Types of arguments#

Required Arguments#

Keyword Arguments (**kwargs)#

Default Arguments#

Variable-length Arguments#

Functions

Creating a function

Function Calling

The return statement

Arguments in function

Call by reference in Python

Types of arguments

Required Arguments

Keyword Arguments (**kwargs)

Default Arguments

Variable-length Arguments