How Do * and Unpack Arguments in Python Functions?

Unpacking Arguments in Python: Navigating and *

Unpacking Single Sequences: The Role of *

A single asterisk (*) plays a crucial role in unpacking a sequence or collection into positional arguments. Consider the following example:

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

values = (1, 2)

s = add(*values)  # Equivalent to: s = add(1, 2)

By using the * operator, we effectively unpack the values tuple and pass its elements (1 and 2) as arguments to the add function. This is particularly useful when working with variable-length sequences.

Unpacking Dictionaries: The Power of **

The double asterisk (**) serves a similar purpose but for dictionaries, allowing you to provide values for named arguments. Take this example:

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

Here, the ** operator unpacks the values dictionary, extracting the key-value pairs and using them to set the corresponding keyword arguments in the add function call.

Synergy of and *

It's noteworthy that both operators can be combined in the same function call. Consider the following scenario:

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

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

s = add(*values1, **values2)  # Equivalent to: s = sum(1, 2, c=10, d=15)

This call effectively unpacks values1 into the first two positional arguments (a and b), and values2 into the remaining keyword arguments (c and d).

Implementation and Performance Implications:
Python implements this behaviour through a combination of function argument binding and dynamic call generation. Using and * allows for the flexible calling of functions with variable-length arguments, leading to code that is both concise and versatile. However, it's important to note that excessive use of these operators can potentially impact performance, particularly when combined with high-frequency function calls.

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