python histogram one-liner
Python 3.x does have reduce, you just have to do a from functools import reduce. It also has "dict comprehensions", which have exactly the syntax in your example.
Python 2.7 and 3.x also have a Counter class which does exactly what you want:
from collections import Countercnt = Counter("abracadabra")In Python 2.6 or earlier, I'd personally use a defaultdict and do it in 2 lines:
d = defaultdict(int)for x in xs: d[x] += 1That's clean, efficient, Pythonic, and much easier for most people to understand than anything involving reduce.
It's kinda cheaty to import modules for oneliners, so here's a oneliner that is O(n) and works at least as far back as Python2.4
>>> f=lambda s,d={}:([d.__setitem__(i,d.get(i,0)+1) for i in s],d)[-1]>>> f("ABRACADABRA"){'A': 5, 'R': 2, 'B': 2, 'C': 1, 'D': 1}And if you think __ methods are hacky, you can always do this
>>> f=lambda s,d=lambda:0:vars(([setattr(d,i,getattr(d,i,0)+1) for i in s],d)[-1])>>> f("ABRACADABRA"){'A': 5, 'R': 2, 'B': 2, 'C': 1, 'D': 1}:)