通过Python将大字符串分割成包含'n'个单词的多个子字符串

Question

源文本：美国独立宣言

怎么把上面的源文本分成几个小部分，每部分包含'n'个单词呢？

我用split(' ')来提取每个单词，但我不知道怎么一次性处理多个单词。

我可以遍历我得到的单词列表，然后通过把单词粘在一起（同时加上空格）来创建另一个列表。不过，我觉得我的方法不太符合Python的风格。

Answer 1

对于很长的字符串，建议使用迭代器，这样可以更快并且占用更少的内存。

import re, itertools

# Original text
text = "When in the course of human Events, it becomes necessary for one People to dissolve the Political Bands which have connected them with another, and to assume among the Powers of the Earth, the separate and equal Station to which the Laws of Nature and of Nature?s God entitle them, a decent Respect to the Opinions of Mankind requires that they should declare the causes which impel them to the Separation."
n = 10

# An iterator which will extract words one by one from text when needed
words = itertools.imap(lambda m:m.group(), re.finditer(r'\w+', text))
# The final iterator that combines words into n-length groups
word_groups = itertools.izip_longest(*(words,)*n)

for g in word_groups: print g

将会得到以下结果：

('When', 'in', 'the', 'course', 'of', 'human', 'Events', 'it', 'becomes', 'necessary')
('for', 'one', 'People', 'to', 'dissolve', 'the', 'Political', 'Bands', 'which', 'have')
('connected', 'them', 'with', 'another', 'and', 'to', 'assume', 'among', 'the', 'Powers')
('of', 'the', 'Earth', 'the', 'separate', 'and', 'equal', 'Station', 'to', 'which')
('the', 'Laws', 'of', 'Nature', 'and', 'of', 'Nature', 's', 'God', 'entitle')
('them', 'a', 'decent', 'Respect', 'to', 'the', 'Opinions', 'of', 'Mankind', 'requires')
('that', 'they', 'should', 'declare', 'the', 'causes', 'which', 'impel', 'them', 'to')
('the', 'Separation', None, None, None, None, None, None, None, None)

Answer 2

你想创建n-grams吗？我来告诉你我是怎么做的，使用的是NLTK这个工具。

punct = re.compile(r'^[^A-Za-z0-9]+|[^a-zA-Z0-9]+$')
is_word=re.compile(r'[a-z]', re.IGNORECASE)
sentence_tokenizer = nltk.data.load('tokenizers/punkt/english.pickle')
word_tokenizer=nltk.tokenize.punkt.PunktWordTokenizer()

def get_words(sentence):
    return [punct.sub('',word) for word in word_tokenizer.tokenize(sentence) if is_word.search(word)]

def ngrams(text, n):
    for sentence in sentence_tokenizer.tokenize(text.lower()):
        words = get_words(sentence)
        for i in range(len(words)-(n-1)):
            yield(' '.join(words[i:i+n]))

然后

for ngram in ngrams(sometext, 3):
    print ngram

Answer 3

text = """
When in the course of human Events, it becomes necessary for one People to dissolve the Political Bands which have connected them with another, and to assume among the Powers of the Earth, the separate and equal Station to which the Laws of Nature and of Nature?s God entitle them, a decent Respect to the Opinions of Mankind requires that they should declare the causes which impel them to the Separation.

We hold these Truths to be self-evident, that all Men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty, and the pursuit of Happiness?-That to secure these Rights, Governments are instituted among Men, deriving their just Powers from the Consent of the Governed, that whenever any Form of Government becomes destructive of these Ends, it is the Right of the People to alter or abolish it, and to institute a new Government, laying its Foundation on such Principles, and organizing its Powers in such Form, as to them shall seem most likely to effect their Safety and Happiness. Prudence, indeed, will dictate that Governments long established should not be changed for light and transient Causes; and accordingly all Experience hath shewn, that Mankind are more disposed to suffer, while Evils are sufferable, than to right themselves by abolishing the Forms to which they are accustomed. But when a long Train of Abuses and Usurpations, pursuing invariably the same Object, evinces a Design to reduce them under absolute Despotism, it is their Right, it is their Duty, to throw off such Government, and to provide new Guards for their future Security. Such has been the patient Sufferance of these Colonies; and such is now the Necessity which constrains them to alter their former Systems of Government. The History of the Present King of Great-Britain is a History of repeated Injuries and Usurpations, all having in direct Object the Establishment of an absolute Tyranny over these States. To prove this, let Facts be submitted to a candid World.
"""

words = text.split()
subs = []
n = 4
for i in range(0, len(words), n):
    subs.append(" ".join(words[i:i+n]))
print subs[:10]

这段代码会输出：

['When in the course', 'of human Events, it', 'becomes necessary for one', 'People to dissolve the', 'Political Bands which have', 'connected them with another,', 'and to assume among', 'the Powers of the', 'Earth, the separate and', 'equal Station to which']

或者，使用列表推导式的写法：

subs = [" ".join(words[i:i+n]) for i in range(0, len(words), n)]