What does the Double Star operator mean in Python?

The double star/asterisk (*) operator has more than one meaning in Python. We can use it as a exponential operator, used as function *kwargs, unpacking the iterables, and used to Merge the Dictionaries.

Exponential operator

For numeric data the double asterisk (**) is used as an exponential operator. Let's take an example and see how the double star operator works on numeric operands.

Example

The following example uses double asterisks/star (**) to calculate “a to the power b” and it works equivalent to the pow() function.

a = 10
b = 2
result = a ** b
print("a**b = ", result)

Output

a**b =  100

Creating a function with **kwargs

At the time of defining a function the double asterisk(**) is used to create a Python function with an arbitrary number of keyword arguments. It is nothing but a function that can accept any number of key−word arguments.

Example

The above example is defined to take any number of keyword arguments.

def fun(**kwargs):
    for k, v in kwargs.items():
        print('key = {}, value = {}'.format(k,v))

fun(a=10, b=2, c=9, d=3, e=6)

Output

key = a, value = 10
key = b, value = 2
key = c, value = 9
key = d, value = 3
key = e, value = 6

Unpacking the iterables

When calling a function, the double asterisk/star (**) operator can be used as a parameter to unpack the keyword arguments.

To unpack the key as well as the values together from a Python dictionary, we can use the double−asterisk operator.

Example

Using double star (**) operator we have unpacked the dictionary and sent the key value pairs to a function which accepts arbitrary number of keyword arguments.

def foo(**kwargs):
    for key, value in kwargs.items():
        if value > 90:
            print(str(key) + " " + str(value))

d =  {'a': 100, 'b': 20, 'c': 96, 'd':101}
foo(**d)

Output

a 100
c 96
d 101

Merging the Dictionaries

By using the double star/asterisk operator we can merge two dictionaries in Python.

Syntax

New_dict = {**dict1, **dict2} 

The above syntax can create a new dictionary by unpacking the key−value pairs of existing dictionaries. If any duplicate keys present those are automatically resolved by this method.

Example

The following example demonstrates how to merge the dictionaries, and double asterisk before dictionary object **dict can be used to unpack the dictionary.

d1 = {'A': 10, 'B': 20}
d2 = {'C': 30, 'D': 40}
print('initial dictionaries d1 = {} and d2 = {}: '.format(d1,d2))

z = {**d1, **d2} 
print("Merged dictionary: ", z)

Output

initial dictionaries d1 = {'A': 10, 'B': 20} and d2 = {'C': 30, 'D': 40}
Merged dictionary:  {'A': 10, 'B': 20, 'C': 30, 'D': 40}