python counter helper

counterdict.py

#!/usr/bin/env python3

import collections

class counterdict(collections.defaultdict):
  def __init__(self):
    collections.defaultdict.__init__(self, counterdict)

  def __sub__(self, value):
    """Upgrade this counter to a number.
    """
    return -value

  def __add__(self, value):
    """Upgrade this counter to a number.
    """
    return value

  def dict(self):
    out = {}
    for k, v in self.items():
      if isinstance(v, counterdict):
        out[k] = v.dict()
      else:
        out[k] = v
    return out


if __name__ == '__main__':
  x = counterdict()
  x['z'] -= 1
  x['abc'] += 1
  x['def'] += 10
  x['butts']['hello'] += 20
  x['butts']['what']['the'] = 1

  print(x)
  print(x.dict())