Question

有点python newb在这里试图弄清楚为什么我的代码没有给出预期的结果。首先是代码：

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 permutations方法来创建word_list的排列。但是，我不想要所有的排列。我只想要逗号和单词'和'在word_list中保持其原始位置/索引的排列，并将这些排列附加到permuted_list。

我正在使用代码行if comma_AND_indices == observed_comma_AND_indices: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permuted_list时，我发现不会保留逗号和“和”，但会附加所有排列。

（您可能想知道为什么在函数中使用grammar_list会感到烦恼，但这里的代码是稍微大一点的脚本的一部分，其中grammar_list扮演其角色）

任何有助于对此表示赞赏的帮助。

的Darren

编辑：这是一个打印出来的样本：

[('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，尽管您可以更加简洁地生成相同的列表，product()和[','] + 3 + ['and']的排列[w for w in word_list if w not in (',', 'and')]，生成相同的120 * 24 = 2880种组合。

如果您只期望120个结果，那么您忘记了您没有在输出中测试3个逗号和单词'and'的顺序;允许该列表有24种不同的排列：

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

换句话说，对于名词的任何给定排列，你使用3个逗号和单词and在不同位置产生24个变体的句子。

仅生成120种名词组合：

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])

Answer 2

如果重复无关紧要，您可以使用itertools.product：

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

打印哪些：

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

但是既然他们这样做了，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)

它基本上可以在正确的位置创建所有可能的单词排序，循环遍历所有的词性，并将句子“叠加”在一起。

Python itertools排列通过索引比较缩小结果，不按预期工作

2 个答案: