Optional Parameters

In python we can give optional parameters that we can decide if we want to pass or not.

• we use * to indicate if parameter is optional or not

def log(message, *values):
    pass

• here first param message is required.
• after first message parameter, any number of subsequent parameters are optional.
• function's body doesn't need to change, only callers will change in different scenarios.

import datetime

def log(message, *values):
    if not values:
        print(message)
    else:
        values_str = ', '.join(str(x) for x in values)
        print("%s: %s" % (message, values_str))

log("helo")
log("my numbers are ",1,2,3)
log("current date is ", datetime.datetime.now())

• if we want to pass some list values as optional arguments we can directly do so using * operator

def log(message, *values):
    if not values:
        print(message)
    else:
        values_str = ', '.join(str(x) for x in values)
        print("%s: %s" % (message, values_str))
        
l = [1,12.3,'hello']
log()

• Issue: variable arguments are always turned into tuple before they are passed to function(here log function) so if we use * operator on a generator, it will try to create a tuple of all values generator will yield. if tuple grows so much in size, program may fail.

• Another usability issue with optional parameters is if my function structure is func(a,b, *args) and function is being used at multiple places where different optional params were set to it from time to time. Now if i want to add a positional argument then I have to add it before *args and that means whereever I have passed optional params till now, i have to go and change the definition there.