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

deffun():print("Welcome to GFG")# Driver code to call a functionfun()

Output

Welcome to GFG

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.

Syntax for functions with arguments:

def function_name(parameter: data_type) -> return_type:
"""Docstring"""
# body of the function
return expression

data_typeandreturn_typeare optional in function declaration, meaning the same function can also be written as:

def function_name(parameter) :
"""Docstring"""
# body of the function
return expression

Let's understand this with an 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

defevenOdd(x:int)->str:if(x%2==0):return"Even"else:return"Odd"print(evenOdd(16))print(evenOdd(7))

Output

EvenOdd

The above function can also be declared withouttype_hints, like this:

Python

defevenOdd(x):if(x%2==0):return"Even"else:return"Odd"print(evenOdd(16))print(evenOdd(7))

Output

EvenOdd

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

Adefault 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

defmyFun(x,y=50):print("x: ",x)print("y: ",y)myFun(10)

Output

x:  10y:  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

defstudent(fname,lname):print(fname,lname)student(fname='Geeks',lname='Practice')student(lname='Practice',fname='Geeks')

Output

Geeks PracticeGeeks Practice

Positional Arguments

We used thePosition 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

defnameAge(name,age):print("Hi, I am",name)print("My age is ",age)print("Case-1:")nameAge("Suraj",27)print("\nCase-2:")nameAge(27,"Suraj")

Output

Case-1:Hi, I am SurajMy age is  27Case-2:Hi, I am 27My age is  Suraj

Arbitrary Keyword Arguments

In Python Arbitrary Keyword Arguments,*args, and **kwargs can pass a variable number of arguments to a function using special symbols. There are two special symbols:

*args in Python (Non-Keyword Arguments)
**kwargs in Python (Keyword Arguments)

Example 1: Variable length non-keywords argument

Python

defmyFun(*argv):forarginargv:print(arg)myFun('Hello','Welcome','to','GeeksforGeeks')

Output

HelloWelcometoGeeksforGeeks

Example 2:Variable length keyword arguments

Python

defmyFun(**kwargs):forkey,valueinkwargs.items():print("%s ==%s"%(key,value))myFun(first='Geeks',mid='for',last='Geeks')

Output

first == Geeksmid == forlast == Geeks

Docstring

The first string after the function is called the Document string orDocstring in short. This is used to describe the functionality of the function. The use of docstring in functions is optional but it is considered a good practice.

The below syntax can be used to print out the docstring of a function.

Syntax: print(function_name.__doc__)

Example:Adding Docstring to the function

Python

defevenOdd(x):"""Function to check if the number is even or odd"""if(x%2==0):print("even")else:print("odd")print(evenOdd.__doc__)

Output

Function to check if the number is even or odd

Python Function within Functions

A function that is defined inside another function is known as theinner function ornested function. Nested functions can access variables of the enclosing scope. Inner functions are used so that they can be protected from everything happening outside the function.

Python

deff1():s='I love GeeksforGeeks'deff2():print(s)f2()f1()

Output

I love GeeksforGeeks

Anonymous Functions in Python

In Python, ananonymous function means that a function is without a name. As we already know the def keyword is used to define the normal functions and the lambda keyword is used to create anonymous functions.

Python

defcube(x):returnx*x*x# without lambdacube_l=lambdax:x*x*x# with lambdaprint(cube(7))print(cube_l(7))

Output

Return Statement in Python Function

Thereturnstatement in Python is used to exit a function and send a value back to the caller. It can return anydata type, and if multiple values are separated by commas, they are automatically packed into atuple. If no value is specified, the function returnsNoneby default.

Syntax:

return [expression]

Explanation:

return:Ends the function and optionally sends a value to the caller.
[expression]:Optional value to return, defaults to None if omitted.

Example: Python Function Return Statement

Python

defsquare_value(num):"""This function returns the square    value of the entered number"""returnnum**2print(square_value(2))print(square_value(-4))

Output

For more information, refer to this article: Python return statement

Pass by Reference and Pass by Value

One important thing to note is, in Python every variable name is a reference. When we pass a variable to a function Python, a new reference to the object is created. Parameter passing in Python is the same as reference passing in Java.

Python

# Here x is a new reference to same list lstdefmyFun(x):x[0]=20# Driver Code (Note that lst is modified# after function call.lst=[10,11,12,13,14,15]myFun(lst)print(lst)

Output

[20, 11, 12, 13, 14, 15]

When we pass a reference and change the received reference to something else, the connection between the passed and received parameters is broken. For example, consider the below program as follows:

Python

defmyFun(x):x=[20,30,40]lst=[10,11,12,13,14,15]myFun(lst)print(lst)

Output

[10, 11, 12, 13, 14, 15]

Another example demonstrates that the reference link is broken if we assign a new value (inside the function).

Python

defmyFun(x):x=20x=10myFun(x)print(x)

Output

Exercise: Try to guess the output of the following code.

Python

defswap(x,y):temp=xx=yy=tempx=2y=3swap(x,y)print(x)print(y)

Output

Recursive Functions in Python

Recursionin Python refers to when a function calls itself. There are many instances when you have to build a recursive function to solveMathematical and Recursive Problems.

Using a recursive function should be done with caution, as a recursive function can become like a non-terminating loop. It is better to check your exit statement while creating a recursive function.

Python

deffactorial(n):ifn==0:return1else:returnn*factorial(n-1)print(factorial(4))