Python create functions / classes with variables at don't need to be passed in and have default values

Question

I often use **kwargs when I am creating a function, and then (in the event the user does not pass in a variable) I set a default value with a try and except statement like this:

def function(**kwargs):

    # Set a default value for 'start_date' if no value passed into the function
    try: start_date = kwargs['start_date']
    except KeyError: start_date = '2022-01-01'

I am pretty convinced this is not best practice. For example when using Pandas DataFrames if a variable is not specified a default value is used.

Eg:

df.drop(['column_a'], inplace=True)

If 'inplace' is not specified it defaults to False. How can i reproduce this?

Answer 1

Instead of using **kwargs you can provide default arguments, which is what they are intended for, which will allow optional parameters

def function(start_date='2022-01-01'):
    print(start_date)

>>> function('2022-04-19')  # arg
2022-04-19
>>> function(start_date='2022-02-04')  # kwarg
2022-02-04
>>> function()  # default value
2022-01-01

with the other advantage being implicit validation of arguments which **kwargs would otherwise happily accept

>>> function(wrong=10)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: function() got an unexpected keyword argument 'wrong'