我认为PlaintextCorpusReader，至少在你的输入语言是英语的情况下，已经使用punkt标记器对输入进行了细分。
PlainTextCorpusReader的构造函数
def __init__(self, root, fileids,
word_tokenizer=WordPunctTokenizer(),
sent_tokenizer=nltk.data.LazyLoader(
'tokenizers/punkt/english.pickle'),
para_block_reader=read_blankline_block,
encoding='utf8'):
你可以向读者传递一个单词和句子标记器，但是后者的默认值已经是nltk.data.LazyLoader('tokenizers/punkt/english.pickle')。
对于单个字符串，将按以下方式使用标记器（此处说明，有关punkt标记器，请参见第5节）。
>>> import nltk.data
>>> text = """
... Punkt kNows that the periods in Mr. Smith and Johann S. Bach
... do not mark sentence boundaries. And sometimes sentences
... can start with non-capitalized words. i is a good variable
... name.
... """
>>> tokenizer = nltk.data.load('tokenizers/punkt/english.pickle')
>>> tokenizer.tokenize(text.strip())
如果你的目录如下所示：
newcorpus/
file1.txt
file2.txt
...
import os
from nltk.corpus.reader.plaintext import PlaintextCorpusReader
corpusdir = 'newcorpus/' # Directory of corpus.
newcorpus = PlaintextCorpusReader(corpusdir, '.*')
注意：该PlaintextCorpusReader将会使用默认设置，nltk.tokenize.sent_tokenize()并将nltk.tokenize.word_tokenize()你的文本分为句子和单词，并且这些功能是针对英语构建的，可能不适用于所有语言。
这是创建测试文本文件的完整代码，以及如何使用NLTK创建语料库以及如何在不同级别访问语料库：
import os
from nltk.corpus.reader.plaintext import PlaintextCorpusReader
# Let's create a corpus with 2 texts in different textfile.
txt1 = """This is a foo bar sentence.\nAnd this is the first txtfile in the corpus."""
txt2 = """Are you a foo bar? Yes I am. Possibly, everyone is.\n"""
corpus = [txt1,txt2]
# Make new dir for the corpus.
corpusdir = 'newcorpus/'
if not os.path.isdir(corpusdir):
os.mkdir(corpusdir)
# Output the files into the directory.
filename = 0
for text in corpus:
filename+=1
with open(corpusdir+str(filename)+'.txt','w') as fout:
print>>fout, text
# Check that our corpus do exist and the files are correct.
assert os.path.isdir(corpusdir)
for infile, text in zip(sorted(os.listdir(corpusdir)),corpus):
assert open(corpusdir+infile,'r').read().strip() == text.strip()
# Create a new corpus by specifying the parameters
# (1) directory of the new corpus
# (2) the fileids of the corpus
# NOTE: in this case the fileids are simply the filenames.
newcorpus = PlaintextCorpusReader('newcorpus/', '.*')
# Access each file in the corpus.
for infile in sorted(newcorpus.fileids()):
print infile # The fileids of each file.
with newcorpus.open(infile) as fin: # Opens the file.
print fin.read().strip() # Prints the content of the file
print
# Access the plaintext; outputs pure string/basestring.
print newcorpus.raw().strip()
print
# Access paragraphs in the corpus. (list of list of list of strings)
# NOTE: NLTK automatically calls nltk.tokenize.sent_tokenize and
# nltk.tokenize.word_tokenize.
#
# Each element in the outermost list is a paragraph, and
# Each paragraph contains sentence(s), and
# Each sentence contains token(s)
print newcorpus.paras()
print
# To access pargraphs of a specific fileid.
print newcorpus.paras(newcorpus.fileids()[0])
# Access sentences in the corpus. (list of list of strings)
# NOTE: That the texts are flattened into sentences that contains tokens.
print newcorpus.sents()
print
# To access sentences of a specific fileid.
print newcorpus.sents(newcorpus.fileids()[0])
# Access just tokens/words in the corpus. (list of strings)
print newcorpus.words()
# To access tokens of a specific fileid.
print newcorpus.words(newcorpus.fileids()[0])
最后，要阅读文本目录并创建其他语言的NLTK语料库，你必须首先确保你拥有一个python-callable单词标记化和句子标记化模块，这些模块接受字符串/基字符串输入并产生以下输出：
>>> from nltk.tokenize import sent_tokenize, word_tokenize
>>> txt1 = """This is a foo bar sentence.\nAnd this is the first txtfile in the corpus."""
>>> sent_tokenize(txt1)
['This is a foo bar sentence.', 'And this is the first txtfile in the corpus.']
>>> word_tokenize(sent_tokenize(txt1)[0])
['This', 'is', 'a', 'foo', 'bar', 'sentence', '.']
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