Python迭代工具排列，通过索引比较缩小结果，而不是预期的工作。

Question

这里的python试图找出为什么我的代码没有给出预期的结果。第一，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，我使用迭代工具排列方法来创建word_list的排列。然而，我不想要所有的排列。我只想让逗号和单词‘和’保持它们在word_list中的原始位置/索引的排列，并将它们附加到permuted_list中。

我正在使用代码行if comma_AND_indices == observed_comma_AND_indices:来筛选出我不想要的那些排列，但是它不起作用，我也不明白为什么。在打印permuted_list时，我发现逗号和‘和’没有保留，但是所有的排列都附加在后面。

(您可能想知道为什么要在函数中使用grammar_list，但是这里的代码是一个稍微大一点的脚本的一部分，grammar_list在其中扮演它的角色)

对此有任何帮助，表示感谢。

达伦

编辑:这是为我打印出来的内容的示例：

[('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'), 

Answer 1

您的代码工作得很好，尽管您可以更快地生成相同的列表--这里使用product()表示[','] + 3 + ['and']和[w for w in word_list if w not in (',', 'and')]的排列，从而产生相同的120 * 24 = 2880组合。

如果您只期望得到120个结果，那么您就会忘记，您没有测试输出中的3个逗号和单词'and'的顺序；允许对该列表进行24种不同的排列：

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

换句话说，对于任何给定的名词排列，你都会在不同的位置用三个逗号和单词and产生24个变体。

只产生名词的120个组合：

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])

Answer 2

如果复制不重要，你可以只使用itertools.product

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

其中的指纹：

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

但既然他们这么做了，你就得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)

从本质上说，它创造了所有可能的顺序词的正确位置，循环通过所有部分的词性，并“叠”在一起的句子。