Dev Notes

Software Development Resources by David Egan.

Declare Default Values for Mutable Types in Python

David Egan

If you want to specify a default for a function argument of an immutable type in Python, you assign the default in the function declaration.

You can’t assign a default value for an immutable type in this way. Instead, you can assign a default value None and check for this inside the function - if the passed-in argument is None, then assign a default:

#!/usr/bin/env python3
class Node:
    def __init__(self, children: dict=None, is_end=False, text=''):
        # If a dict is passed in, set self.children to this, otherwise
	# set it to an empty dict.
	self.children = children if children else dict()
        self.is_end = is_end
        self.text = text

    def print(self):
        print("is_end: {}, text: {}".format(self.is_end, self.text))
        for key in self.children:
            print("Key: {} Value: {}".format(key, self.children[key]))

def main():
    a = Node()
    b = Node({'a': 'value'}, True, 'hello!')


if __name__ == '__main__':

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