How Do * and Unpack Arguments in Python Function Calls?

Unpacking Arguments with and in Python Function Calls*

In Python function calls, the asterisk () and double asterisk (*) operators play significant roles in unpacking sequences and dictionaries into positional or named arguments, respectively.

Single Star (*) Unpacking:

The single asterisk operator (*) unpacks a sequence or collection into positional arguments. Consider the following function:

def add(a, b):
    return a + b

Given a tuple of values values = (1, 2), we can unpack the tuple and pass its elements to the add function using the * operator:

s = add(*values)

This is equivalent to writing:

s = add(1, 2)

Double Star () Unpacking:**

The double asterisk operator (**) follows a similar principle but operates on dictionaries. It unpacks a dictionary's key-value pairs into named arguments:

values = { 'a': 1, 'b': 2 }
s = add(**values)

This is equivalent to:

s = add(a=1, b=2)

Combined Unpacking:

Both operators can be used simultaneously in a single function call. For instance, given the function:

def sum(a, b, c, d):
    return a + b + c + d

And two sets of values:

values1 = (1, 2)
values2 = { 'c': 10, 'd': 15 }

We can unpack these values as follows:

s = add(*values1, **values2)

This is equivalent to:

s = sum(1, 2, c=10, d=15)

Performance Implications:

Using the and * unpacking operators generally has minimal performance implications. However, if the sequence or dictionary being unpacked is large, additional overhead may be incurred during the unpacking process. This is negligible for most practical scenarios.

Equivalent Method:

As an alternative to using the unpacking operators, you can also use the *args and **kwargs syntax, respectively:

def add(*args, **kwargs):
    s = 0
    for arg in args:
        s += arg
    for key, value in kwargs.items():
        s += value

Ultimately, the choice between using the unpacking operators or *args/**kwargs depends on your code style and preference.

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