Python itertools排列通过索引比较缩小了结果范围，没有按预期工作

有些python新手试图弄明白为什么我的代码没有给出预期的结果。首先是守则：

from itertools import permutations

word_list = ['eggs', ',', 'bacon', ',', 'chicken', ',', 'cheese', 'and', 'tomatoes']
grammar_list = ['NOUN', ',', 'NOUN', ',', 'NOUN', ',', 'NOUN', 'AND', 'NOUN']

def permute_nouns():
    permuted_list = []
    comma_AND_indices = [index for index, p in enumerate(grammar_list) if p == "," or p == "AND"]
    # so 'comma_AND_indices' = [1, 3, 5, 7]

    for perm in permutations(word_list):
        observed_comma_AND_indices = [index for index, p in enumerate(perm) if p == "," or p == "and"]
        if comma_AND_indices == observed_comma_AND_indices:
            # what goes wrong here? not matches from list compare above still get appended below.
            permuted_list.append(perm)

    print permuted_list

permute_nouns()

在这个函数中，我使用itertools排列方法创建

单词列表的排列

。然而，我不想要所有的排列。我只想要逗号和单词“and”在

单词列表中保持其原始位置/索引的排列，并将它们附加到
排列列表中

我使用代码行
如果逗号和_索引==观察到的_逗号和_索引：
来过滤掉我不想要的那些排列，但它不起作用，我不明白为什么。在打印出
排列列表时
我发现逗号和“and”没有被保留，但所有排列都被追加

（您可能想知道为什么要在函数中使用
grammar\u list
，但是这里的代码是一个稍大的脚本的一部分，在这个脚本中
grammar\u list
起到了作用）

任何有助于阐明这一点的人都将不胜感激

达伦

编辑：以下是为我打印的内容示例：

[('eggs', ',', 'bacon', ',', 'chicken', ',', 'cheese', 'and', 'tomatoes'), ('eggs', ',', 'bacon', ',', 'chicken', ',', 'tomatoes', 'and', 'cheese'), ('eggs', ',', 'bacon', ',', 'chicken', 'and', 'cheese', ',', 'tomatoes'), ('eggs', ',', 'bacon', ',', 'chicken', 'and', 'tomatoes', ',', 'cheese'), ('eggs', ',', 'bacon', ',', 'cheese', ',', 'chicken', 'and', 'tomatoes'), ('eggs', ',', 'bacon', ',', 'cheese', ',', 'tomatoes', 'and', 'chicken'), ('eggs', ',', 'bacon', ',', 'cheese', 'and', 'chicken', ',', 'tomatoes'), ('eggs', ',', 'bacon', ',', 'cheese', 'and', 'tomatoes', ',', 'chicken'), ('eggs', ',', 'bacon', ',', 'tomatoes', ',', 'chicken', 'and', 'cheese'), ('eggs', ',', 'bacon', ',', 'tomatoes', ',', 'cheese', 'and', 'chicken'), ('eggs', ',', 'bacon', ',', 'tomatoes', 'and', 'chicken', ',', 'cheese'), ('eggs', ',', 'bacon', ',', 'tomatoes', 'and', 'cheese', ',', 'chicken'), ('eggs', ',', 'bacon', ',', 'chicken', ',', 'cheese', 'and', 'tomatoes'), ('eggs', ',', 'bacon', ',', 'chicken', ',', 'tomatoes', 'and', 'cheese'), ('eggs', ',', 'bacon', ',', 'chicken', 'and', 'cheese', ',', 'tomatoes'), ('eggs', ',', 'bacon', ',', 'chicken', 'and', 'tomatoes', ',', 'cheese'), ('eggs', ',', 'bacon', ',', 'cheese', ',', 'chicken', 'and', 'tomatoes'), ('eggs', ',', 'bacon', ',', 'cheese', ',', 'tomatoes', 'and', 'chicken'), ('eggs', ',', 'bacon', ',', 'cheese', 'and', 'chicken', ',', 'tomatoes'), ('eggs', ',', 'bacon', ',', 'cheese', 'and', 'tomatoes', ',', 'chicken'), ('eggs', ',', 'bacon', ',', 'tomatoes', ',', 'chicken', 'and', 'cheese'), ('eggs', ',', 'bacon', ',', 'tomatoes', ',', 'cheese', 'and', 'chicken'), ('eggs', ',', 'bacon', ',', 'tomatoes', 'and', 'chicken', ',', 'cheese'), ('eggs', ',', 'bacon', ',', 'tomatoes', 'and', 'cheese', ',', 'chicken'), ('eggs', ',', 'bacon', 'and', 'chicken', ',', 'cheese', ',', 'tomatoes'), ('eggs', ',', 'bacon', 'and', 'chicken', ',', 'tomatoes', ',', 'cheese'), ('eggs', ',', 'bacon', 'and', 'chicken', ',', 'cheese', ',', 'tomatoes'), ('eggs', ',', 'bacon', 'and', 'chicken', ',', 'tomatoes', ',', 'cheese'), ('eggs', ',', 'bacon', 'and', 'cheese', ',', 'chicken', ',', 'tomatoes'), ('eggs', ',', 'bacon', 'and', 'cheese', ',', 'tomatoes', ',', 'chicken'), ('eggs', ',', 'bacon', 'and', 'cheese', ',', 'chicken', ',', 'tomatoes'), ('eggs', ',', 'bacon', 'and', 'cheese', ',', 'tomatoes', ',', 'chicken'), ('eggs', ',', 'bacon', 'and', 'tomatoes', ',', 'chicken', ',', 'cheese'), ('eggs', ',', 'bacon', 'and', 'tomatoes', ',', 'cheese', ',', 'chicken'), ('eggs', ',', 'bacon', 'and', 'tomatoes', ',', 'chicken', ',', 'cheese'), ('eggs', ',', 'bacon', 'and', 'tomatoes', ',', 'cheese', ',', 'chicken'), ('eggs', ',', 'chicken', ',', 'bacon', ',', 'cheese', 'and', 'tomatoes'), ('eggs', ',', 'chicken', ',', 'bacon', ',', 'tomatoes', 'and', 'cheese'), ('eggs', ',', 'chicken', ',', 'bacon', 'and', 'cheese', ',', 'tomatoes'), ('eggs', ',', 'chicken', ',', 'bacon', 'and', 'tomatoes', ',', 'cheese'), ('eggs', ',', 'chicken', ',', 'cheese', ',', 'bacon', 'and', 'tomatoes'), ('eggs', ',', 'chicken', ',', 'cheese', ',', 'tomatoes', 'and', 'bacon'), ('eggs', ',', 'chicken', ',', 'cheese', 'and', 'bacon', ',', 'tomatoes'), ('eggs', ',', 'chicken', ',', 'cheese', 'and', 'tomatoes', ',', 'bacon'), ('eggs', ',', 'chicken', ',', 'tomatoes', ',', 'bacon', 'and', 'cheese'), ('eggs', ',', 'chicken', ',', 'tomatoes', ',', 'cheese', 'and', 'bacon'), ('eggs', ',', 'chicken', ',', 'tomatoes', 'and', 'bacon', ',', 'cheese'), ('eggs', ',', 'chicken', ',', 'tomatoes', 'and', 'cheese', ',', 'bacon'), ('eggs', ',', 'chicken', ',', 'bacon', ',', 'cheese', 'and', 'tomatoes'), ('eggs', ',', 'chicken', ',', 'bacon', ',', 'tomatoes', 'and', 'cheese'), ('eggs', ',', 'chicken', ',', 'bacon', 'and', 'cheese', ',', 'tomatoes'), ('eggs', ',', 'chicken', ',', 'bacon', 'and', 'tomatoes', ',', 'cheese'), ('eggs', ',', 'chicken', ',', 'cheese', ',', 'bacon', 'and', 'tomatoes'), ('eggs', ',', 'chicken', ',', 'cheese', ',', 'tomatoes', 'and', 'bacon'), ('eggs', ',', 'chicken', ',', 'cheese', 'and', 'bacon', ',', 'tomatoes'), 

您的代码运行得很好，尽管您可以更快地生成相同的列表，使用
['，']+3+['和']
和
[w在word_列表中，如果w不在（'，'和'）]
中，则更简洁地生成相同的列表，生成相同的120*24=2880组合

如果您只希望得到120个结果，那么您忘记了您没有测试输出中3个逗号和单词
”和“
的顺序；该列表允许有24种不同的排列：

>>> len(list(permutations([','] * 3 + ['and'])))
24

换句话说，对于任何给定的仅仅是名词的排列，你产生了24种句子变体，其中有3个逗号，单词
和
位于不同的位置

要生成120个名词组合：

nouns = [w for w in word_list if w not in (',', 'and')]
grammar = [w for w in word_list if w in (',', 'and')]
result = []
for perm in permutations(nouns):
    result.append([w for word, g in map(None, perm, grammar) for w in (word, g) if w is not None])

如果副本不重要，您可以使用
itertools.product
：

for words in itertools.product(*(['a'], ['big', 'fat'], ['dog', 'house'])):
    print(' '.join(words))

其中打印：

a big dog
a big house
a fat dog
a fat house

但既然他们这么做了，你就必须做一些更复杂的事情：

import itertools
import collections

grammar = ['NOUN', ',', 'NOUN', ',', 'NOUN', ',', 'NOUN', 'AND', 'NOUN']
parts_of_speech = {
    'NOUN': ['eggs', 'bacon', 'chicken', 'cheese', 'tomatoes'],
    'AND': ['and'],
    ',': [',']
}

def partial_sentences(words, indices, sentence_length):
    if len(indices) > len(words):
        orderings = itertools.product(words, repeat=len(indices))
    else:
        orderings = itertools.permutations(words, len(indices))

    for words in orderings:
        sentence = [None] * sentence_length

        for index, word in zip(indices, words):
            sentence[index] = word

        yield sentence

def pos_stacks(parts_of_speech, grammar):
    positions = collections.defaultdict(list)

    for index, pos in enumerate(grammar):
        positions[pos].append(index)

    for pos, indices in positions.items():
        yield partial_sentences(parts_of_speech[pos], indices, len(grammar))

for result in itertools.product(*pos_stacks(parts_of_speech, grammar)):
    sentence = [next(itertools.ifilter(bool, words)) for words in zip(*result)]

    print(sentence)

基本上，它在适当的位置创建单词的所有可能顺序，在所有词类中循环，并将句子“堆叠”在一起。
为什么不去掉逗号和
和
s。这样会更有效率。我无法重现你的问题；我看到2880个版本符合您的标准，而总排列为362880个。您介意发布预期输出的一部分吗？我已经添加了部分打印输出，您将看到“和”改变了位置。这就是说，我现在注意到逗号保持着它们的位置，除非逗号和大便指向它们应该在的位置。