使用Python

Question

如何在python中找出表达式的深度？我编写的代码适用于[[1,2],[1,2,[3,6,54]]等输入，但不适用于depth (['+', ['expt', 'x', 2], ['expt', 'y', 2]]) => 2和depth(('/', ('expt', 'x', 5), ('expt', ('-', ('expt', 'x', 2), 1), ('/', 5, 2)))) => 4

等输入

a=0
k=0
j=0
maxli=[] 
li =[[1,2],[1,2,[3,6,54]] # list whose depth is to be found
#print len(li)

def depth(x):


    global a,k,j
    j=j+1
    print" j's value is ",j
    for i in x:

      for h in range(len(li)): # runs loop through the items of the list 
          if i== li[h]  : k=0  

      if isinstance(i,(tuple,list)) == True: #if we find that there is list
        k=k+1

      #  print "this is for item",i  
      #  print k
        depth(i) 

    a=k
    maxli.append(a) # putting the values of a in maxli

depth(li)
print "The depth of tree is :",max(maxli)

Answer 1

这里使用递归的正确方法是通过函数的返回值，而不是通过操纵全局变量。您可以定义这样的深度函数：

def is_list(x):
    return hasattr(x,'__getitem__') and type(x) != str

def depth(l):
    if not is_list(l): return 0
    maxdepth = 0
    for elem in l:
        maxdepth = max(maxdepth, depth(elem))
    return maxdepth + 1