Filtering defaultdict with dictionary comprehension

Question

I have a defaultdict where keys are a number and values are lists with two entries each. I want to filter by a condition based on the first entry. I tried using the suggestion here: filter items in a python dictionary where keys contain a specific string

Here is the code I used:

circuits = {k:v for k,v in circuits.iteritems() if (v[0]+weightlimit <= histotal) in k}

After this code ran, I got an error about a missing key in the only spot in my code where I use the dictionary.

This of course means something is wrong, because a defaultdict does not do that. So it seems that the dictionary comprehension will change the defaultdict to a dictionary.

What is the best course of action here? Is it more efficient to use a different method of filtering, or is it more efficient to somehow cast my dictionary to defaultdict? And what's a good way of doing either?

Thank you!

Please do not post links to code. Post code as formatted text in the question itself. Provide a [mcve] — juanpa.arrivillaga, Feb 17 '18 at 04:43

score 2 · Accepted Answer · answered Feb 17 '18 at 04:36

A dict comprehension produces just that—a dict. Because you filtered, it's a dict now—not a defaultdict. You'll need to wrap it in a defaultdict if you want that behavior.

Unless there's a strong need for performance in this block, just stick to that approach. It's cleanest. But don't prematurely optimize. Profile your code and speed up the slow parts.

Filtering defaultdict with dictionary comprehension

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