Extract a Sentence Containing a Word Using Python… As well as the sentences around it?

Question

There are a bunch of questions that get at extracting a particular sentence that contains a word (like extract a sentence using python and Python extract sentence containing word ), and I have enough beginner experience with NLTK and SciPy to be able to do that on my own.

However, I'm getting stuck trying to extract a sentence containing a word... as well as the sentences before and after the target sentence.

For example:

"I was walking along to school the other day, when it began to rain. I reached for my umbrella, but I realized I had forgotten it at home. What could I do? I immediately ran for the nearest tree. But then I realized I couldn't stay try with a tree without any leaves."

In this example, the target word is "could." If I wanted to extract the target sentence ( What could I do? ) as well as the preceding and following sentences ( I reached for my umbrella, but I realized I had forgotten it at home. and I immediately ran for the nearest tree. ), what would be a good approach?

Assume I have each paragraph sectioned off as its own text...

for paragraph in document:
    do something

... is there a proper way to tackle this question? I have about 10,000 paragraphs with varying numbers of sentences around the target word (which appears is every single paragraph).

Answer 1

What about something like this?

import nltk.data
tokenizer = nltk.data.load('tokenizers/punkt/english.pickle')
for paragraph in document:
    paragraph_sentence_list = tokenizer.tokenize(paragraph)
    for line in xrange(0,len(paragraph_sentence_list)):
        if 'could' in paragraph_sentence_list[line]:

            print(paragraph_sentence_list[line])

            try:
                print(paragraph_sentence_list[line-1])
            except IndexError as e:
                print('Edge of paragraph. Beginning.')
                pass

            try:
                print(paragraph_sentence_list[line+1])
            except IndexError as e:
                print('Edge of paragraph. End.')
                pass

What this does is break the paragraphs into a list of sentences.

The iterating over the sentences tests if 'could' is in the setence. If it is, then it prints the previous index [line-1], the current index [line] and the next index [line+1]

Answer 2

Make use of sent_tokenize to extract sentences from raw corpus and then word_tokenize to tokenize the sentences and then extract the sentences with "could":

>>> from nltk.corpus import brown
>>> from nltk import sent_tokenize, word_tokenize
>>> corpus = " ".join(brown.words())
>>> [i for i in sent_tokenize(corpus) if u"could" in word_tokenize(i)]

To get the sentence before and after:

>>> sentences = sent_tokenize(corpus)
>>> [" ".join([sentences[i-1], j, sentences[i+1]]) for i,j in enumerate(sentences) if u"could" in word_tokenize(j)]