python - python中的霍夫曼代码不能正常工作

Question

我的一位教授给了我下面的代码。我让它按照我想的方式对齐，但问题是代码没有按应有的方式工作。我不明白为什么。任何形式的帮助将不胜感激。

import sys
codes = {}
def frequency (str):
    freqs = {}
    for ch in str :
        freqs[ch] = freqs.get(ch,0) + 1
    return freqs


def sortFreq (freqs) :
    letters = freqs.keys()
    tuples = []
    for let in letters :
        tuples.append((freqs[let],let))
    tuples.sort()
    return tuples


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] # the branch points freq
        tuples = theRest + [(combFreq,leastTwo)] # add branch point to the end
        tuples.sort(key=lambda tup: tup[0], reverse=False) # sort it into place
    return tuples[0] # Return the single tree inside the list


def trimTree (tree) :
# Trim the freq counters off, leaving just the letters
    p = tree[1] # ignore freq count in [0]
    if type(p) == type("") : return p # if just a leaf, return it
    else : return (trimTree(p[0]), trimTree(p[1])) # trim left then right and recombine


def assignCodes (node, pat='') :
    global codes
    if type(node) == type("") :
        codes[node] = pat # A leaf. set its code
    else : #
        assignCodes(node[0], pat+"0") # Branch point. Do the left branch
        assignCodes(node[1], pat+"1") # then do the right branch.


def encode (str) :
    global codes
    output = ""
    for ch in str : output += codes[ch]
    return output


def decode (tree, str) :
    output = ""
    p = tree
    for bit in str :
        if bit == '0' : p = p[0] # Head up the left branch
        else : p = p[1] # or up the right branch
        if type(p) == type("") :
            output += p # found a character. Add to output
            p = tree # and restart for next character
    return output


def main () :
    debug = True
    str_init = sys.stdin.read()
    str = str_init[0:len(str_init)-1]
    freqs = frequency(str)
    tuples = sortFreq(freqs)
    tree = buildTree(tuples)
    if debug : print("Built tree", tree)
    tree = trimTree(tree)

    if debug : print("Trimmed tree", tree)
    assignCodes(tree)

    if debug : print(codes)
    small = encode(str)
    original = decode (tree, small)
    print("Original text length", len(str))

    print("Requires %d bits. (%d bytes)" % (len(small), (len(small)+7)/8))
    print("Restored matches original", str == original)

if __name__ == "__main__" : main()

当我通过命令行调用文件时，上面的代码将让我写出我想要处理的短语，但是当我按下回车键时根本没有答案。我在评论中被告知要添加此代码的特定输入和所需输出。就是这样，输入“你好”并期望输出

Built tree (5, ((2, ((1, 'e'), (1, 'h'))), (3, ((1, 'o'), (2, 'l')))))
Trimmed tree (('e', 'h'), ('o', 'l'))
{'e': '00', 'h': '01', 'o': '10', 'l': '11'}
Original text length 5
Requires 10 bits. (2 bytes)
Restored matches original True

标签： pythonhuffman-code