Args and kwargs

args and kwargs can be used in Python to pass leftover arguments in a function

example¶

def to_uppercase(input):
    return input.upper()

we can do to_upppercase("test"), but if we do to_upppercase("test", "123") our function will break.
Now you might say, the dev messed up, using the code like that. And you are right!

But sometimes we want to support this way of using code, e.g. in abstract functions where you don’t know all the ways the user will use the methods. e.g in PySide

class MyCustomWidget(QtWidgets.QWidget):
    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)

In PySide, we can use args and kwargs to pass all arguments supported by QWidget, without having to rewrite them all ourself.
I can still do MyCustomWidget(parent=my_parent) without Python throwing an exception.

*args catches all undefined arguments (an array)
***kwargs catches all undefined keyword arguments (a dict)

Python
software architecture

Backlinks¶

figmapy development review
- I spent a lot of time adding kwargs to methods.
  … and their inherited methods.
  Mainly because i wanted autocomplete to work.
  Given the time cost for keeping the methods updated, next time I’ll use args and kwargs.