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Understanding args and kwargs in Python: Best Practices and Guide

When we see the documentation of any function that contains *args and **kwargs, have you ever wondered – What are these strange parameters passed inside that function?

As an example:

function(params, *args, **kwargs)

As a beginner, you might get confused about how to use that function or what to pass as an argument in place of *args and **kwargs when calling that function.

Well not to worry, in this tutorial we gonna discuss *args and **kwargs – What they mean and their uses in the function with examples that help you to understand better.

And we gonna see the glimpse of * and ** (Unpacking operators) used in the examples.

Introduction

The function in Python helps us to write code that is reused, to perform particular tasks in various operations.

Let’s define a function that prints the character names.

Example: function that prints character names

Output

The function characters above takes 3 positional arguments name1name2name3 and simply prints the names.

What if we pass more than the number of arguments that it takes

What do you think the output would be, the output will be a TypeError.

The error was raised because of the extra argument passed inside the function, which only accepts three arguments.

That’s unfortunate because we need to pass one more argument inside the function character in order for the code to run without error.

However, this is not the best practice. For example, suppose you are working on a project where you need to add multiple arguments dynamically when calling a specific function.

What should you do in such situations? There is a way to deal with such situations.

Usage of *args

*args is simply shortened for arguments. It is used as an argument when we are not sure how many arguments should we pass in the function.

The (*) asterisk before the args ensures that the argument has a variable length.

*args is a Non-keyword argument or Positional argument.

By using *args, you are allowed to pass any number of arguments when calling a function.

Example: Using *args in function definition

Output

We got Tuple because when we use *args the function will get the arguments as tuple.

If we check the type.

Output

We can also use regular arguments with *args.

Example: Using regular arguments and args in the function definition

Output

Note: You can use any name you want instead of args, including your pet’s name, a friend’s name, or even your girlfriend’s name, as long as you put a * before it.

Example: Using a different name instead of args

Output

There is one exception: when passing regular arguments and *args as parameters to a function, never pass *args before regular arguments.

Example: Using *args before regular argument inside the function

Output

We got a TypeError because we cannot pass *args before the regular argument.

There will be no error if we change the code and move the parameters passed inside the function.

Output

The above code was executed without any error.

Usage of **kwargs

**kwargs is shortened for Keyword argument.

Now you are familiar with *args and know its implementation, **kwargs works similarly as *args.

But unlike *args**kwargs takes keyword or named arguments.

In **kwargs, we use ** double asterisk that allows us to pass through keyword arguments.

Example: Using **kwargs in the function definition

Output

The type of **kwargs is Dictionary i.e., the arguments accepted as key-value.

Example: Using regular argument and **kwargs together inside the function definition

Output

Just like *args, you can choose any name instead of **kwargs

Example: Using a different name instead of kwargs

Output

Note: We cannot pass **kwargs before *args in the function definition otherwise, we’ll get a SyntaxError.

The convention should be – function(params, *args, **kwargs)

Example

We can use all three types of arguments inside the function definition and in this example, we’ll see the use of the unpacking operator – * and **.

Output

You’ll notice that the variables called names and roles in the above code were used.

However, we put * before the names variable and ** before the roles variable when we passed them inside the function.

These are the Unpacking operators.

Unpacking Operator

These operators come quite in handy as you saw above.

* single asterisk is used to unpack iterable and ** double asterisk is used to unpack dictionary.

The * iterable unpacking operator and ** dictionary unpacking operators to allow unpacking in more positions, an arbitrary number of times, and in additional circumstances. Specifically, in function calls, in comprehensions and generator expressions, and in displays. Source

To know more, click here


Conclusion

So far you will now be able to implement the fundamentals of *args and **kwargs inside the functions.

These might come in handy when you are working on projects where data comes dynamically in a function and you don’t know how many arguments to be passed in that function. This makes your project scalable.


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That’s all for now

Keep Coding✌✌.