Chapter 6.2 default arguments.md

Chapter 6.2: Default parameters in functions

Table of Contents:

• Chapter 6.2: Default parameters in functions
  • Introduction

Introduction

While defining function, we can add default values to some or all parameters so that it takes default value when we do not pass values while calling the function. We need to add default parameters only after required parameters are added otherwise it raises an exception

Example 1: A program that can add either 2 or 3 numbers

def add_numbers(a, b, c = 0):
    return a + b + c

print(add_numbers(1, 2))        # 3
print(add_numbers(1, 2, 3))     # 6

Here, in this example, if we pass 2 arguments (1,2), the default value of c is already 0 so when we call function, it does not give us exception.

If we try to define required parameters after default parameters, then it raises an exception.

def add_numbers(a=0, b, c):
    return a + b + c
# SyntaxError: non-default argument follows default argument

Example 2: internationalization

def greet(key, lang='en'):
    words = {
            'hello': {
                'en': 'Hello',
                'fr': 'Bonjour',
                'np': 'नमस्कार',
                'jp': 'こにちは'
            },
            'bye': {
                'en': 'Bye',
                'fr': 'au revoir',
                'np': 'फेरी भेटौला',
                'jp': 'さよなら'
            }
        }
    print(words[key][lang])
greet('hello')          # Hello (default value of lang is 'en')
greet('hello', 'fr')    # Bonjour
greet('hello', 'np')    # नमस्कार