Python : How to Unpack List, Tuple or Dictionary to Function arguments using * and **

Unpack elements in a list or tuple to function arguments

Args(*)
Kwargs(**)

1)Args(*)

In Python function definitions, the special syntax *args is used to pass a variable number of arguments to a function. It is used to pass a variable-length, non-keyworded argument list.

To take in a variable number of arguments, the syntax is to use the symbol *; by convention, it is often used with the word args.
*args enables you to accept more arguments than the number of formal arguments you previously defined. With *args, you can add any number of extra arguments to your existing formal parameters (including zero extra arguments).
For instance, suppose we want to create a multiply function that can take any number of arguments and multiply them all together. It is possible.

Example:

i) Unpacking a list

Below is the implementation:

# givenlist
givenlist = ['hello', 'this', 'is', 'BTechGeeks']
# unpack the list
print(*givenlist)

Output:

hello this is BTechGeeks

ii)Unpacking a tuple

Below is the implementation:

# giventuple
giventuple = ('hello', 'this', 'is', 'BTechGeeks')
# unpack the tuple
print(*giventuple)

Output:

hello this is BTechGeeks

However, we must ensure that the elements of the list or tuple are exactly equal to function parameters. Otherwise, it will result in an error. As a result, it is commonly used with functions that accept variable length arguments.

Below is the implementation:

def calculateSum(*args):
    # Arguments of variable length are accepted by this function.
    num = len(args)
    if num == 0:
        return 0
    sumargs = 0
    for element in args:
        sumargs += element
    return sumargs


list1 = [1, 2, 3]
# passing list to calculateSum function
print(calculateSum(*list1))
list2 = [1, 2, 3, 4, 5, 6, 7]
# passing list to calculateSum function
print(calculateSum(*list2))

Output:

6
28

2)Kwargs(**)

In Python function definitions, the special syntax **kwargs is used to pass a keyworded, variable-length argument list. We call ourselves kwargs with a double star. The reason for this is that the double star allows us to pass keyword arguments through (and any number of them).

** is another symbol provided by Python. When it is prefixed with a dictionary, all of the key value pairs in the dictionary are unpacked to function arguments.

Examples:

Below is the implementation:

def printDict(price, name, Model):
    print("price =", price)
    print("name =", name)
    print("Model =", Model)


# given dictionary
dictionary = {'price': 100, 'name': 'Apple', 'Model': '12pro'}
# printing dictionary arguments using kwargs**
printDict(**dictionary)

Output:

price = 100
name = Apple
Model = 12pro

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