Python Functions is a block of statements that return the specific task. The idea is to put some commonly or repeatedly done tasks together and make a function so that instead of writing the same code again and again for different inputs, we can do the function calls to reuse code contained in it over and over again.
Some Benefits of Using Functions
- Increase Code Readability
- Increase Code Reusability
Python Function Declaration
The syntax to declare a function is:
Syntax of Python Function Declaration
Types of Functions in Python
Below are the different types of functions in Python:
- Built-in library function: These are Standard functions in Python that are available to use.
- User-defined function: We can create our own functions based on our requirements.
Creating a Function in Python
We can define a function in Python, using the def keyword. We can add any type of functionalities and properties to it as we require. By the following example, we can understand how to write a function in Python. In this way we can create Python function definition by using def keyword.
Python
# A simple Python function
def fun():
print("Welcome to GFG")
Calling a Function in Python
After creating a function in Python we can call it by using the name of the functions Python followed by parenthesis containing parameters of that particular function. Below is the example for calling def function Python.
Python
# A simple Python function
def fun():
print("Welcome to GFG")
# Driver code to call a function
fun()
Output:
Welcome to GFG
Python Function with Parameters
If you have experience in C/C++ or Java then you must be thinking about the return type of the function and data type of arguments. That is possible in Python as well (specifically for Python 3.5 and above).
Python Function Syntax with Parameters
def function_name(parameter: data_type) -> return_type:
"""Docstring"""
# body of the function
return expression
The following example uses arguments and parameters that you will learn later in this article so you can come back to it again if not understood.
Python
def add(num1: int, num2: int) -> int:
"""Add two numbers"""
num3 = num1 + num2
return num3
# Driver code
num1, num2 = 5, 15
ans = add(num1, num2)
print(f"The addition of {num1} and {num2} results {ans}.")
Output:
The addition of 5 and 15 results 20.
Note: The following examples are defined using syntax 1, try to convert them in syntax 2 for practice.
Python
# some more functions
def is_prime(n):
if n in [2, 3]:
return True
if (n == 1) or (n % 2 == 0):
return False
r = 3
while r * r <= n:
if n % r == 0:
return False
r += 2
return True
print(is_prime(78), is_prime(79))
Output:
False True
Python Function Arguments
Arguments are the values passed inside the parenthesis of the function. A function can have any number of arguments separated by a comma.
In this example, we will create a simple function in Python to check whether the number passed as an argument to the function is even or odd.
Python
# A simple Python function to check
# whether x is even or odd
def evenOdd(x):
if (x % 2 == 0):
print("even")
else:
print("odd")
# Driver code to call the function
evenOdd(2)
evenOdd(3)
Output:
even
odd
Types of Python Function Arguments
Python supports various types of arguments that can be passed at the time of the function call. In Python, we have the following function argument types in Python:
- Default argument
- Keyword arguments (named arguments)
- Positional arguments
- Arbitrary arguments (variable-length arguments *args and **kwargs)
Let’s discuss each type in detail.
Default Arguments
A default argument is a parameter that assumes a default value if a value is not provided in the function call for that argument. The following example illustrates Default arguments to write functions in Python.
Python
# Python program to demonstrate
# default arguments
def myFun(x, y=50):
print("x: ", x)
print("y: ", y)
# Driver code (We call myFun() with only
# argument)
myFun(10)
Output:
x: 10
y: 50
Like C++ default arguments, any number of arguments in a function can have a default value. But once we have a default argument, all the arguments to its right must also have default values.
Keyword Arguments
The idea is to allow the caller to specify the argument name with values so that the caller does not need to remember the order of parameters.
Python
# Python program to demonstrate Keyword Arguments
def student(firstname, lastname):
print(firstname, lastname)
# Keyword arguments
student(firstname='Geeks', lastname='Practice')
student(lastname='Practice', firstname='Geeks')
Output:
Geeks Practice
Geeks Practice
Positional Arguments
We used the Position argument during the function call so that the first argument (or value) is assigned to name and the second argument (or value) is assigned to age. By changing the position, or if you forget the order of the positions, the values can be used in the wrong places, as shown in the Case-2 example below, where 27 is assigned to the name and Suraj is assigned to the age.
Python