CODEWITHSUNDEEP
python
f. c.
f. c.

Reputation: 1145

What is the python way to avoid a default argument as a list of Nones?

I have two filenames as input arguments. Both filenames go through the same process, and their default values are None. I write my function like this:

import logging

def my_func(filename_list=[None]*2):
    for i in filename_list:
         if i is None:
             logging.info('One filename is None')
         else:
             # do stuff

Is there a better way to do it in python instead of using [None]*2?

Upvotes: 0

Views: 80

Answers (2)

chepner
chepner

Reputation: 532418

Just use None as the default value. You can create a list of None inside the file.

def my_func(filename_list=None):
    if filename_list is None:
        filename_list = [None, None]

    for i in filename_list:
        ...

What is special about a list of 2 Nones, though? If my_func always takes a list of 2 filenames, I would recommend just passing them explicitly:

def my_func(file1=None, file2=None):
     for i in [file1, file2]:
         ...

Otherwise, an empty list would seem reasonable:

def my_func(filename_list=None):
    if file_name_list is None:
        filename_list = []
    for i in filename_list:
        ...

Upvotes: 1

Welgriv
Welgriv

Reputation: 833

The most pythonic way is:

import logging

def my_func(first_filename, second_filename):
    file_names = [first_filename, second_filename]
    for i in filename_list:
         if i is None:
             logging.info('One filename is None')
         else:
             # do stuff

If you know you have 2 files for sure each call, do not pass a list as argument. There is no point.

Upvotes: 1

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