Is there a way to make a nested dictionary such that I can say mydict[x][y][z] += 1, where mydict[x][y][z] did not previously exist, and defaults to 0 (and would be 1 after incrementing)?
I looked into answers to a similar question in which you can say mydict[x][y][z] = 1 using defaultdict from the collections class (Declaring a multi dimensional dictionary in python), but this does not allow you to assume a default value and then increment.
Yes, you can do this with the collections module:
from collections import defaultdict, Counter
d = defaultdict(lambda: defaultdict(lambda: Counter()))
d['A']['B']['C'] += 1
# defaultdict(<function __main__.<lambda>>,
# {'A': defaultdict(<function __main__.<lambda>.<locals>.<lambda>>,
# {'B': Counter({'C': 1})})})
Note this is also possible via only using nested defaultdict:
d = defaultdict(lambda: defaultdict(lambda: defaultdict(int)))
However, given Counter was created for the specific purpose of incrementing integers, this would be the method I prefer.