Ryan Scott Brown

I build cloud-based systems for startups and enterprises. My background in operations gives me a unique focus on writing observable, reliable software and automating maintenance work.

I love learning and teaching about Amazon Web Services, automation tools such as Ansible, and the serverless ecosystem. I most often write code in Python, TypeScript, and Rust.

B.S. Applied Networking and Systems Administration, minor in Software Engineering from Rochester Institute of Technology.

    Fun With **kwargs

    Ever want to write functions that flexibly receive arguments? What about getting defaults from a configuration on the module level, then have those defaults automatically used by functions in your module?

    Well kwargs might be just what you need. “kwarg” is a nickname for “keyword arguments”, which you’re likely already familiar with in a format like this:

    def func(first='ask questions', second='shoot'):
        print '{0} first'.format(first)
        print '{0} second'.format(second)
    if __name__ == '__main__':

    Let’s try it out!

    $ python test.py
    ask questions first
    shoot second

    Now that’s all well and good, of course, but what if you you need to set those defaults on the fly, say, from a config file that your program reads on startup. Let’s say your config file looks like this.

    first = shoot
    second = ask_questions

    And this is the code that will read the config.

    from ConfigParser import ConfigParser
    conf = ConfigParser()
    conf_dict = dict(conf.items('Defaults'))
    def func(**kwargs):
        # the name selected for kwargs is not important, what's special is the **
        # any arguments we need that weren't in kwargs, get them from conf_dict
        print '{0} first'.format(kwargs['first'])
        print '{0} second'.format(kwargs['second'])
    if __name__ == '__main__':
        print 'maybe something more conservative...'
        func(second='more questions', first='ask questions')

    The program now gives different output.

    $ python with_kwargs.py
    shoot first
    ask questions second
    maybe something more conservative...
    ask questions first
    more questions second

    An alternative to having default arguments from a config file would be something like this. The values remain hardcoded, unfortunately, but it allows you to have defaults for kwargs.

    def func(**kwargs):
        # the .get() function takes a second argument, which is returned by default
        # if there is no value for that key
        print '{0} first'.format(kwargs.get('first', 'shoot'))
        print '{0} second'.format(kwargs.get('second', 'ask questions'))

    So now we have a program that does a similar thing to our original, but none of the defaults are hardcoded (except the config file, but let’s ignore that).

    The uses of **kwargs go beyond this, of course, they’re great for making extremely flexible functions that are tolerant to non-consistent use.

    Design by Sam Lucidi (samlucidi.com)