How to output NLTK pos_tag in the string instead of a list?

Question

I need to run nltk.pos_tag on a large dataset and need to have its output like the one that is offered by Stanford tagger.

For example while running the following code I have;

import nltk
text=nltk.word_tokenize("We are going out.Just you and me.")
print nltk.pos_tag(text)

the output is: [('We', 'PRP'), ('are', 'VBP'), ('going', 'VBG'), ('out.Just', 'IN'), ('you', 'PRP'), ('and', 'CC'), ('me', 'PRP'), ('.', '.')]

In the case that I need it to be like:

 We/PRP are/VBP going/VBG out.Just/NN you/PRP and/CC me/PRP ./.

I prefer to not using string functions and need a dirrect output because the amount of the text is so high and it adds lots of time complexities to the processing

Answer 1

In short:

' '.join([word + '/' + pos for word, pos in tagged_sent]

In long:

I think you're overthinking about using string functions to concat the strings, it's really not that expensive.

import time
from nltk.corpus import brown

tagged_corpus = brown.tagged_sents()

start = time.time()

with open('output.txt', 'w') as fout:
    for i, sent in enumerate(tagged_corpus):
        print(' '.join([word + '/' + pos for word, pos in sent]), end='\n', file=fout)

end = time.time() - start
print (i, end)

It took 2.955 seconds on my laptop for all 57339 sentences from the brown corpus.

[out]:

$ head -n1 output.txt 
The/AT Fulton/NP-TL County/NN-TL Grand/JJ-TL Jury/NN-TL said/VBD Friday/NR an/AT investigation/NN of/IN Atlanta's/NP$ recent/JJ primary/NN election/NN produced/VBD ``/`` no/AT evidence/NN ''/'' that/CS any/DTI irregularities/NNS took/VBD place/NN ./.

But using string to concatenate the word and POS can cause trouble later on when you need to read your tagged output, e.g.

>>> from nltk import pos_tag
>>> tagged_sent = pos_tag('cat / dog'.split())
>>> tagged_sent_str = ' '.join([word + '/' + pos for word, pos in tagged_sent])
>>> tagged_sent_str
'cat/NN //CD dog/NN'
>>> [tuple(wordpos.split('/')) for wordpos in tagged_sent_str.split()]
[('cat', 'NN'), ('', '', 'CD'), ('dog', 'NN')]

If you want to saved the tagged output and then read it later, it's better to use pickle to save the tagged_output, e.g.

>>> import pickle
>>> tagged_sent = pos_tag('cat / dog'.split())
>>> with open('tagged_sent.pkl', 'wb') as fout:
...     pickle.dump(tagged_sent, fout)
... 
>>> tagged_sent = None
>>> tagged_sent
>>> with open('tagged_sent.pkl', 'rb') as fin:
...     tagged_sent = pickle.load(fin)
... 
>>> tagged_sent
[('cat', 'NN'), ('/', 'CD'), ('dog', 'NN')]