Скачать или смотреть How to Properly Call Functions with Standard Arguments, *args, and **kwargs in Python

Learn how to correctly call functions in Python using standard arguments, `*args`, and `**kwargs` by understanding the proper syntax to avoid common errors.
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This video is based on the question https://stackoverflow.com/q/76508431/ asked by the user 'vasili111' ( https://stackoverflow.com/u/1601703/ ) and on the answer https://stackoverflow.com/a/76508493/ provided by the user 'Ori Yarden PhD' ( https://stackoverflow.com/u/16785596/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding Function Arguments in Python

In Python, functions can take various types of arguments, making it essential to understand how to utilize them effectively. Among these, you have standard arguments (positional), variadic arguments (*args), and keyword arguments (**kwargs). This guide will address a common issue developers face when calling a function that requires all three types of parameters, illustrating how to do it correctly and avoid common pitfalls.

The Problem: A Syntax Error

Consider the following code snippet, which is intended to invoke a function with standard arguments and additional arguments using *args and **kwargs:

[[See Video to Reveal this Text or Code Snippet]]

This results in the following error:

[[See Video to Reveal this Text or Code Snippet]]

Why Does This Error Occur?

In Python, the order of arguments is crucial when calling a function:

Normal (positional) arguments must come before any keyword arguments.

You cannot mix keyword arguments with positional arguments that come after them.

In our example, while val1 and val2 are specified as keyword arguments, the subsequent strings "a", "b", and "c" are treated as positional arguments. This leads to the SyntaxError above.

The Solution: Correcting the Function Call

To resolve this issue and call the function correctly while using val1 and val2 as named arguments, you need to adjust the order in which you define your function. Here's how to correctly redefine your function with *args and the named parameters placed after:

[[See Video to Reveal this Text or Code Snippet]]

Outcome

When you run the corrected function call, you get:

[[See Video to Reveal this Text or Code Snippet]]

This displays the values of val1 and val2 alongside the elements stored in *args and **kwargs, successfully meeting your requirements.

Tips for Using *args and **kwargs

Flexibility: Use *args when you want to pass a variable number of arguments (like a list of items). They're unpacked into a tuple.

Named Arguments: Use **kwargs when you want to pass keyword arguments that can be accessed as a dictionary.

Order Matters: Always keep in mind the order while declaring your function. Positional arguments - *args - named arguments - **kwargs.

Conclusion

Understanding how to manipulate function arguments in Python allows for more dynamic and flexible code. By correctly calling functions with standard arguments, *args, and **kwargs, we can enhance our programming capabilities. Taking care of the order and syntax while passing arguments prevents common errors and increases the readability of our code. Happy coding!