How to fix this ValueError? - python-3.x

Question

I am trying to run a python code, mostly based on NLTK book, for ngram POS Tagging a Gujarati language text from my GujaratiTextCorpus. I encountered a ValueError.
I am working with Python 3.7.3 in Windows 10. I use jupyter notebook through anaconda. I am a beginner in using python. I studied the answers available on stackoverflow. com to fix my ValueError, but could not solve it.
import nltk
f = open('C:\\Users\\BHOGAYATA\\Documents\\GujaratiPosTagging\\cts260.txt', encoding = 'utf8')
raw = f.read()
train2_sents = nltk.sent_tokenize(raw)
text2 = nltk.Text(train2_sents)
train2_sents
import nltk
f = open('C:\\Users\\BHOGAYATA\\Documents\\GujaratiPosTagging\\txt42_sents.txt', encoding = 'utf8')
raw = f.read()
bs_sents = nltk.sent_tokenize(raw)
text3 = nltk.Text(bs_sents)
bs_sents
unigram_tagger = nltk.UnigramTagger(train2_sents)
unigram_tagger.tag(bs_sents)
I expected that the words of the two Gujarati sentences would be POS Tagged. I found the following error messages:
ValueError
Traceback (most recent call last)
<ipython-input-3-5fae0b92393e> in <module>
11 text3 = nltk.Text(bs_sents)
12 bs_sents
---> 13 unigram_tagger = nltk.UnigramTagger(train2_sents)
14 unigram_tagger.tag(bs_sents)
15
~\Anaconda3\lib\site-packages\nltk\tag\sequential.py in __init__(self, train, model, backoff, cutoff, verbose)
344
345 def __init__(self, train=None, model=None, backoff=None, cutoff=0, verbose=False):
--> 346 NgramTagger.__init__(self, 1, train, model, backoff, cutoff, verbose)
347
348 def encode_json_obj(self):
~\Anaconda3\lib\site-packages\nltk\tag\sequential.py in __init__(self, n, train, model, backoff, cutoff, verbose)
293
294 if train:
--> 295 self._train(train, cutoff, verbose)
296
297 def encode_json_obj(self):
~\Anaconda3\lib\site-packages\nltk\tag\sequential.py in _train(self, tagged_corpus, cutoff, verbose)
181 fd = ConditionalFreqDist()
182 for sentence in tagged_corpus:
--> 183 tokens, tags = zip(*sentence)
184 for index, (token, tag) in enumerate(sentence):
185 # Record the event.
ValueError: not enough values to unpack (expected 2, got 1)

Answer 1

It says the variable you are passing have one output but you are expecting two..
Ex:
for a, b in [("a", "b")]:
print("a:", a, "b:", b)
This will work
for a, b in [("a")]:
print("a:", a, "b:", b)
This will not work
Edit:
Look at your UnigramTagger
For first argument it takes a list of tagged sentences of type
list(list(tuple(str, str)))
You are giving train2_sents of type
list(tuple(str,str)
Where your
list(tuple(str,str) is same as train2_sents