python - 我需要假设此代码中的 python 为空序列

Question

该函数打印关键字长度，然后打印所需长度的所有字典关键字的排序列表，其中频率最高，其次是频率。例如下面的代码:

 word_frequencies =  {"fish":9,  "parrot":8,  "frog":9,  "cat":9,  "stork":1,  "dog":4, "bat":9,  "rat":4}

 print_most_frequent(word_frequencies,3)
 print_most_frequent(word_frequencies,4)
 print_most_frequent(word_frequencies,5)
 print_most_frequent(word_frequencies,6)
 print_most_frequent(word_frequencies, 7) 

打印输出:

 3 letter keywords: ['bat', 'cat'] 9
 4 letter keywords: ['fish', 'frog'] 9
 5 letter keywords: ['stork'] 1
 6 letter keywords: ['parrot'] 8
 7 letter keywords: [] 0

到目前为止我有这段代码:

def print_most_frequent(words_dict, word_len):
    right_length = {}
    for k, v in words_dict.items():
        if len(k) == word_len:
             right_length[k] = v
    max_freq = max(right_length.values())
    max_words = {}
    for k, v in right_length.items():
         if v == max_freq:
              max_words[k] = v
    print (str(word_len) + " letter keywords: " + str(sorted(max_words.keys())) + " " + str(max_freq))

这给了我:

 3 letter keywords: ['bat', 'cat'] 9
 4 letter keywords: ['fish', 'frog'] 9
 5 letter keywords: ['stork'] 1
 6 letter keywords: ['parrot'] 8

但不是空序列。如何添加到我的代码中，以便它计入空序列。

 7 letter keywords: [] 0

Answer 1

只需向 max() 调用添加一个后备条件，这样它就不会尝试查找空迭代中的最大值:

max_freq = max(right_length.values() or [0])

如果 right_length.values() 为空，则将使用 [0] (不为空)，并且 max() 不会产生错误。