Chapter 6.3 args kwargs.md

Chapter 6.3: Arbitrary arguments in python

Table of Contents:

• Chapter 6.3: Arbitrary arguments in python
  • Background
  • Arbitrary number of arguments
  • Arbitrary number of keyword arguments

Background

As our functions become more and more dynamic, it is not possible to define a function with maximum number of default arguments which makes our code more complicated. Example, we want to be able to add either 3, or 4, or 5 or even 10 arguments.

The Traditional Approach:

def add_numbers(a, b, c=0, d=0, e=0, f=0, g=0):
    return a + b + c + d + e + f + g

print(add_numbers(1,2)) # 3
print(add_numbers(1,2, 3))   # 6
print(add_numbers(1,2, 3, 4))   # 10
print(add_numbers(1,2, 3, 4, 5))    # 15
print(add_numbers(1,2, 3, 4, 5, 6)) # 21

Here, the main problem is default parameters in all optional values which even decreases the code readability. If we could pass dynamic number of arguments, then we did not need to set default values to each variable.

Arbitrary number of arguments

In the above scenario, if we use arbitrary number of arguments, then we could do the following:

def add_numbers(a, b, *args):
    sum_value = a + b
    for item in args:
        sum_value += item
    return sum_value
print(add_numbers(1, 2)) # 3
print(add_numbers(1, 2, 3))   # 6
print(add_numbers(1, 2, 3, 4))   # 10
print(add_numbers(1, 2, 3, 4, 5))    # 15
print(add_numbers(1, 2, 3, 4, 5, 6)) # 21

Here, add_number needs at lease 2 numbers to calculate the sum but is capable of accepting any number of arguments and perform addition

Arbitrary number of keyword arguments

Arbitrary number of keyword arguments are those arguments which are used as named parameters in a function call. They are extra arguments which will be treated as a dictionary whenever we want to access keys and values from it.

def display_student_detail(name, age, **kwargs):
    print(f'[ details of {age} years old student: {name}]')
    for key, value in kwargs.items():
        print(f'The {key} is {value}')

display_student_detail(
    'John Doe', 20,
    subject='Science', class_teacher='John Lennon', address='Singapore'
)

Output:

[ details of 20 years old student: John Doe]
The subject is Science
The class_teacher is John Lennon
The address is Singapore```