python多重继承新算法C3介绍

class B(A)

class B(A1,A2,A3 ...)

class A(O):pass
class B(O):pass
class C(O):pass
class E(A,B):pass
class F(B,C):pass
class G(E,F):pass

mro(E) = [E] + merge(mro(A), mro(B), [A,B])
       = [E] + merge([A,O], [B,O], [A,B])

mro(E) = [E,A,B] + merge([O], [O])
       = [E,A,B,O]

#-*- encoding:GBK -*-# 
def mro_C3(*cls): 
        if len(cls)==1: 
            if not cls[0].__bases__: 
                return  cls 
            else: 
                return cls+ mro_C3(*cls[0].__bases__) 
        else: 
            seqs = [list(mro_C3(C)) for C in cls ] +[list(cls)] 
            res = [] 
            while True: 
              non_empty = list(filter(None, seqs)) 
              if not non_empty: 
                  return tuple(res) 
              for seq in non_empty: 
                  candidate = seq[0] 
                  not_head = [s for s in non_empty if candidate in s[1:]] 
                  if not_head: 
                      candidate = None 
                  else: 
                      break 
              if not candidate: 
                  raise TypeError("inconsistent hierarchy, no C3 MRO is possible") 
              res.append(candidate) 
              for seq in non_empty: 
                  if seq[0] == candidate: 
                      del seq[0]