霍夫曼编码错误

Question

我想实现霍夫曼编码算法。

我写了下面的代码

def make_leaf(symbol,weight): 
    return (symbol,weight) 

def is_leaf(x): 
    return isinstance(x,tuple) and \ 
      len(x)==2 and \ 
      isinstance(x[0],str) and \ 
      isinstance(x[1],int) 

def get_leaf_symbol(leaf): 
    return leaf[0] 

def get_leaf_freq(leaf): 
    return leaf[1] 

def get_left_branch(huff_tree): 
    return huff_tree[0] 

def get_right_branch(huff_tree): 
    return huff_tree[1] 


def get_symbols(huff_tree): 
    if is_leaf(huff_tree): 
     return [get_leaf_symbol(huff_tree)] 
    else: 
     return huff_tree[2] 

def get_freq(huff_tree): 
    if is_leaf(huff_tree): 
     return get_leaf_freq(huff_tree) 
    else: 
     huff_tree[3] 


def make_huffman_tree(left_branch,right_branch): 
    return [left_branch, 
      right_branch, 
      get_symbols(left_branch) + get_symbols(right_branch), 
      get_freq(left_branch) + get_freq(right_branch)] 

然而，当我试图通过编写下面的代码

ht01 = make_huffman_tree(make_leaf('A', 4), 
         make_huffman_tree(make_leaf('B',2), 
              make_huffman_tree(make_leaf('D', 1), 
                 make_leaf('C', 1)))) 

建立二叉树，我得到这样的错误：

Traceback (most recent call last): 
    File "C:\Users\Swadesh\Documents\Anmol\Python\huffman trial.py", line 47, in <module> 
    make_leaf('C', 1)))) 
    File "C:\Users\Swadesh\Documents\Anmol\Python\huffman trial.py", line 41, in make_huffman_tree 
    get_freq(left_branch) + get_freq(right_branch)] 
TypeError: unsupported operand type(s) for +: 'int' and 'NoneType' 

我不知道如何解决这个错误。有人可以帮我吗 ？

感谢

Answer 1

你错过了你的get_freq（）函数的最后一行“回归”。

如果你没有从函数中返回任何东西，Python将使用None作为返回值。

然后，当您尝试在另外使用此返回值时，会发布您发布的错误（您无法将None添加到整数）。