TypeError:“<"在'tuple'和'str'实例之间不支持 [英] TypeError: '<' not supported between instances of 'tuple' and 'str'

问题描述

我有一种构建霍夫曼树的方法，如下所示:

I have a method that build huffman tree which is as follows:

def buildTree(tuples) :
    while len(tuples) > 1 :
        leastTwo = tuple(tuples[0:2])                  # get the 2 to combine
        theRest  = tuples[2:]                          # all the others
        combFreq = leastTwo[0][0] + leastTwo[1][0]     #enter code here the branch points freq
        tuples   = theRest + [(combFreq,leastTwo)]     # add branch point to the end
        tuples.sort()                                  # sort it into place
    return tuples[0]            # Return the single tree inside the list

但是当我使用以下参数输入函数时:

but while I feed the function with following parameter:

[(1, 'b'), (1, 'd'), (1, 'g'), (2, 'c'), (2, 'f'), (3, 'a'), (5, 'e')]

我收到错误消息

  File "<stdin>", line 7, in buildTree
    tuples.sort()
TypeError: '<' not supported between instances of 'tuple' and 'str'

在调试时，我发现错误是在tuples.sort()中.

While debugging I found the error was in tuples.sort().

推荐答案

抛出该错误是因为您以(priority, (node, node))形式创建内部节点.为了获得相同的优先级，Python然后尝试将叶子节点(因此(priority, symbol)节点元组中的第二个元素)中的符号与内部节点的(node, node)元组进行比较:

The error is thrown because you are creating inner nodes in (priority, (node, node)) form. For equal priorities, Python then tries to compare a symbol from a leaf node (so the second element in a (priority, symbol) node tuple) with the (node, node) tuple from an inner node:

>>> inner = (combFreq, leastTwo)
>>> inner
(2, ((1, 'b'), (1, 'd')))
>>> theRest[1]
(2, 'c')
>>> theRest[1] < inner
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: '<' not supported between instances of 'str' and 'tuple'

要构建霍夫曼树，如果要对节点数组进行排序，则只需要按优先级排序，而忽略其余的元组(符号或子节点):

For building a huffman tree, if you want to sort your array of nodes, you only really need to sort on the priority, ignoring the rest of the tuples (symbols or child nodes):

tuples.sort(key=lambda t: t[0])

进行此更正后，您的buildTree()函数将生成一棵树:

With that correction, your buildTree() function produces a tree:

>>> buildTree([(1, 'b'), (1, 'd'), (1, 'g'), (2, 'c'), (2, 'f'), (3, 'a'), (5, 'e')])
(15, ((6, ((3, 'a'), (3, ((1, 'g'), (2, 'c'))))), (9, ((4, ((2, 'f'), (2, ((1, 'b'), (1, 'd'))))), (5, 'e')))))

就我个人而言，我将使用优先级队列，以避免每次都进行排序.请参阅如何在Python中实现优先级队列?

Personally, I'd use a priority queue instead, avoiding sorting each time. See How to implement Priority Queues in Python?

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