import random

class ContextFree(object):
  def __init__(self):
    self.rules = {}
    self.instancemethod = type(self.add_rule)
    self.max_depth = 100
    self.depth = 0

  def add_rule(self, func, prob=1):
    rule_name = func.__name__

    if not rule_name in self.rules:
      self.rules[rule_name] = { 'funcs' : [], 'total' : 0 }

    total = self.rules[rule_name]['total']
    self.rules[rule_name]['funcs'].append([range(total,(prob+total)), func])
    self.rules[rule_name]['total'] += prob

    def augmented_func(self, options={}):
      if not self.depth >= self.max_depth:
        self.depth += 1
        pick = self.determine_rule(rule_name)
        print('Generation', self.depth)
        pick(self)

    self.__dict__[rule_name] = self.instancemethod(augmented_func, self)

  def determine_rule(self, rule_name):
    rule = self.rules[rule_name]
    winning_number = random.randrange(0, self.rules[rule_name]['total'])
    for func in rule['funcs']:
      if winning_number in func[0]:
        return func[1]

cf = ContextFree()

def box(self):
  print('Rule for box1')
  self.box()

cf.add_rule(box)

def box(self):
  print('Rule for box2')
  self.box()

cf.add_rule(box)

cf.box()