Packing and Unpacking Arguments in Python?

PythonServer Side ProgrammingProgramming

If you have done little-bit of programming in python, you have seen the word “**args” and “**kwargs” in python functions. But what exactly they are?

The * and ** operators did different operations which are complementary to each other depending on where we are using them.

So when we are using them in method definition, like -

def __init__(self, *args, **kwargs):

Above operation is called ‘packing” as it pack all the arguments into one single variable that this method call receives into a tuple called args. We can use name other than args, but args is the most common and pythonic way of doing things. To understand why to put in a one single variable, consider below example:

Let’s assume we have a function which takes three arguments and we have a list of size 3 with us that has all the arguments for the function. Now if we simply try to pass list to the function, the call doesn’t work and through an error.

Example 1

#function which takes three argument
def func(a,b,c):
print("{} {} {}".format(a, b, c))

#list of arguments
lst = ['python', 'java', 'csharp']

#passing the list


TypeError: func() missing 2 required positional arguments: 'b' and 'c'

Once we have ‘picked’ variable, then you do things which are not possible with a normal tuple. Args[0], args[1] and args[2] would give us the first, second and third argument respectively. If you convert the args tuple to a list then as we can do operation of modify, delete and alter items in it.

To pass these packed arguments to another method, we need to do unpacking -

def __init__(self, *args, **kwargs):
#some code here
car(VehicleClass, self).__init__(self, *args, **kwargs)
#some code below

Again we have * operator, but this time it’s in the context of a method call. What is does now is explode the args array and call the method as if each variable is independent. Below is another example to get clear understanding -

Example 2

def func1(x, y, z):

def func2(*args):
#Convert args tuple to a list so we can do modification.
args = list(args)
args[0] = 'HTML'
args[1] = 'CSS'
args[2] = 'JavaScript'

func2('Python', 'Java', 'CSharp')



From above output, we are able to change all three arguments before passing them off to func1.

Similarly we can solve the TypeError message found in example1.


#function which takes three argument
def func(a,b,c):
print("{} {} {}".format(a, b, c))

#list of arguments
lst = ['python', 'java', 'csharp']

#passing the list


python java csharp

So incase we don’t know how many arguments need to be passed to a python function, we can use packing to pack all arguments in a tuple.

#Below function uses packing to sum unknown number of arguments
def Sum(*args):
sum = 0
for i in range(0, len(args)):
   sum = sum + args[i]
return sum

#Driver code
print("Function with 2 arguments & Sum is: \n",Sum(9, 12))
print("Function with 5 arguments & Sum is: \n",Sum(2, 3, 4, 5, 6))
print("Function with 6 arguments & Sum is: \n",Sum(20, 30, 40, 12, 40, 54))


Function with 2 arguments & Sum is:
Function with 5 arguments & Sum is:
Function with 6 arguments & Sum is:

Below is another program to demonstrate the use of packing and unpacking both:

#function with three arguments
def func1(x,y,z):
print("Argument One: ",x)
print("\nArgument Two: ",y)
print("\nArgument Three: ",z)

#Packing- All arguments passed to func2 are packed into tuple *args
def func2(*args):
#To do some modification, we need to convert args tuple to list
args = list(args)

#Modifying args[0] & args[1]
args[0] = 'Hello'
args[1] = 'TutorialsPoint'

#Unpacking args and calling func1()

#Driver code
func2("I", "Love", "Coding")


Argument One: Hello

Argument Two: TutorialsPoint

Argument Three: Coding

Use ** for dictionaries

# Program to demonstrate unpacking of dictionary items using **
def func(x,y,z):
print("Dicionary first item: ",x)
print("\nDictionary second item: ",y)
print("\nDictionary third item: ",z)
d = {'x': 27, 'y': 54, 'z': 81}


Dicionary first item: 27

Dictionary second item: 54

Dictionary third item: 81


  • Used in socket programming where we need to send unknown(infinite) number of requests to server.

  • Used in web frameworks like django to send variable arguments to view functions.

  • Used in wrapper functions that require us to pass in variable arguments.

Published on 02-May-2019 13:50:09