Active Mask - image segmentation
The defaultdict in this case is meant to return the next increasing integer each time a new element is encountered in P.flat().  But to also return the same integer each time that same element is found again. You should have encountered the error:


  TypeError: first argument must be callable or None


defaultdict expects a callable. It will call the passed in function each time there is a lookup miss, and set the dict to that value. To fix that error you need to remove the () from the __next__() to leave:

mis = defaultdict(range(1, P.max() + 1).__iter__().__next__)


However this is overly complicated for what it is doing, and can be simplified a bit by recognizing that there is no reason to have the upper limit in the range, it is just an increasing integer which can be done with itertools.count() liike:

import itertools as it
mis = defaultdict(it.count(1).__next__)