How to create a specific default list in defaultdict?

Question

I am trying to build a defaultdict which is initialized with a specific list. Such that if I access the dict using a key that does exist, it will be initialized with a specific list, let's say [True, True, True].

Instead of doing this

my_defaultdict = collections.defaultdict(list)

So, for example, something like this (obviously would not work)

my_defaultdict = collections.defaultdict([True, True, True])

I tried something like this, but this does not work

my_defaultdict = collections.defaultdict(lambda: list[True, True, True])

I looked in this question for a start, but could not figure it out.

ugh! yes. that is correct. I thought i had tried that. Thank you!! — user2015487, May 26 '15 at 15:39
@doublep that needs more parentheses: `list() takes at most 1 argument`. Note that the `lambda` *also* creates a new list each time. — jonrsharpe, May 26 '15 at 15:39

Assem · Accepted Answer · 2015-05-26T16:03:25.253

2

defaultdict's argument should be a function or any callable object:

my_defaultdict = collections.defaultdict(lambda : [True,True,True])

edited May 26 '15 at 16:03

answered May 26 '15 at 15:48

Assem

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How to create a specific default list in defaultdict?

1 Answers1