Python defaultdict and lambda

Question

In someone else\'s code I read the following two lines:

x = defaultdict(lambda: 0)
y = defaultdict(lambda: defaultdict(lambda: 0))

As the a

Answer 1

defaultdict takes a zero-argument callable to its constructor, which is called when the key is not found, as you correctly explained.

lambda: 0 will of course always return zero, but the preferred method to do that is defaultdict(int), which will do the same thing.

As for the second part, the author would like to create a new defaultdict(int), or a nested dictionary, whenever a key is not found in the top-level dictionary.