Python Tutorials · Python Functions

Python *args / **kwargs

Learn all about Python *args / **kwargs in this comprehensive tutorial.

5 min read beginner

Python Arguments

Python Scope

•By default, a function must be called with the correct number of arguments.
•If you do not know how many arguments will be passed into your function, add a * before the parameter name.
•The *args parameter allows a function to accept any number of positional arguments.
•You can combine regular parameters with *args.
•*args is useful when you want to create flexible functions:
•If you do not know how many keyword arguments will be passed into your function, add two asterisks ** before the parameter name.
•The **kwargs parameter allows a function to accept any number of keyword arguments.
•You can combine regular parameters with **kwargs.
•You can use both *args and **kwargs in the same function.
•The * and ** operators can also be used when calling functions to unpack (expand) a list or dictionary into separate arguments.

*args and **kwargs

By default, a function must be called with the correct number of arguments.

However, sometimes you may not know how many arguments that will be passed into your function.

*args and **kwargs allow functions to accept a unknown number of arguments.

Arbitrary Arguments - *args

If you do not know how many arguments will be passed into your function, add a * before the parameter name.

This way, the function will receive a tuple of arguments and can access the items accordingly:

python

def my_function(*kids):  print("The youngest child is " + kids[2])
  my_function("Emil", "Tobias", "Linus")

Note: Arbitrary Arguments are often shortened to *args in Python documentation.

What is *args?

The *args parameter allows a function to accept any number of positional arguments.

Inside the function, args becomes a tuple containing all the passed arguments:

python

def my_function(*args):  print("Type:", type(args))  print("First argument:", args[0])  print("Second argument:", args[1])  print("All arguments:", args)
  my_function("Emil", "Tobias", "Linus")

Using *args with Regular Arguments

You can combine regular parameters with *args.

Regular parameters must come before *args:

python

def my_function(greeting, *names):  for name in names:    print(greeting, name)
  my_function("Hello", "Emil", "Tobias", "Linus")

In this example, "Hello" is assigned to greeting, and the rest are collected in names.

Practical Example with *args

*args is useful when you want to create flexible functions:

python

def my_function(*numbers):  total = 0  for num in numbers:    total += num  return total
  print(my_function(1, 2, 3))print(my_function(10, 20, 30, 40))print(my_function(5))

python

def my_function(*numbers):  if len(numbers) == 0:    return None  max_num = numbers[0]  for num in numbers:    if num > max_num:      max_num = num  return max_num
  print(my_function(3, 7, 2, 9, 1))

Arbitrary Keyword Arguments - **kwargs

If you do not know how many keyword arguments will be passed into your function, add two asterisks ** before the parameter name.

This way, the function will receive a dictionary of arguments and can access the items accordingly:

python

def my_function(**kid):  print("His last name is " + kid["lname"])
  my_function(fname = "Tobias", lname = "Refsnes")

Note: Arbitrary Keyword Arguments are often shortened to **kwargs in Python documentation.

What is **kwargs?

The **kwargs parameter allows a function to accept any number of keyword arguments.

Inside the function, kwargs becomes a dictionary containing all the keyword arguments:

python

def my_function(**myvar):  print("Type:", type(myvar))  print("Name:", myvar["name"])  print("Age:", myvar["age"])  print("All data:", myvar)
  my_function(name = "Tobias", age = 30, city = "Bergen")

Using **kwargs with Regular Arguments

You can combine regular parameters with **kwargs.

Regular parameters must come before **kwargs:

python

def my_function(username, **details):  print("Username:", username)  print("Additional details:")  for key, value in details.items():    print(" ", key + ":", value)
  my_function("emil123", age = 25, city = "Oslo", hobby = "coding")

Combining *args and **kwargs

You can use both *args and **kwargs in the same function.

The order must be: regular parameters *args **kwargs

python

def my_function(title, *args, **kwargs):  print("Title:", title)  print("Positional arguments:", args)  print("Keyword arguments:", kwargs)
  my_function("User Info", "Emil", "Tobias", age = 25, city = "Oslo")

Unpacking Arguments

The * and ** operators can also be used when calling functions to unpack (expand) a list or dictionary into separate arguments.

If you have values stored in a list, you can use * to unpack them into individual arguments:

python

def my_function(a, b, c):  return a + b + c
  numbers = [1, 2, 3]result = my_function(*numbers)  # Same as: my_function(1, 2, 3)print(result)

If you have keyword arguments stored in a dictionary, you can use ** to unpack them:

python

def my_function(fname, lname):  print("Hello", fname, lname)
  person = {"fname": "Emil", "lname": "Refsnes"}my_function(**person)  # Same as: my_function(fname="Emil", lname="Refsnes")

Note: Remember: Use * and ** in function definitions to collect arguments, and use them in function calls to unpack arguments.

Module quiz

2 questions

Which of the following is true about Python *args / **kwargs?

It is strictly typedIt is evaluated at runtimeIt requires explicit memory managementIt is deprecated

What is the most common pitfall when working with Python *args / **kwargs?

SyntaxErrorIndentationErrorNameErrorTypeError

Answer all questions to submit.

Python Arguments

Python Scope

Python *args / **kwargs

AI Summary

*args and **kwargs

Arbitrary Arguments - *args

What is *args?

Using *args with Regular Arguments

Practical Example with *args

Arbitrary Keyword Arguments - **kwargs

What is **kwargs?

Using **kwargs with Regular Arguments

Combining *args and **kwargs

Unpacking Arguments

Module quiz