from collections import Counter


def termsearch(terms): # Searches full inverted index
    if not set(terms).issubset(words):
        return set()
    return reduce(set.intersection,
                  (set(x[0] for x in txtindx)
                   for term, txtindx in finvindex.items()
                   if term in terms),
                  set(texts.keys()) )

def phrasesearch(phrase):
    wordsinphrase = phrase.strip().strip('"').split()
    if not set(wordsinphrase).issubset(words):
        return set()
    #firstword, *otherwords = wordsinphrase # Only Python 3
    firstword, otherwords = wordsinphrase[0], wordsinphrase[1:]
    found = []
    for txt in termsearch(wordsinphrase):
        # Possible text files
        for firstindx in (indx for t,indx in finvindex[firstword]
                          if t == txt):
            # Over all positions of the first word of the phrase in this txt
            if all( (txt, firstindx+1 + otherindx) in finvindex[otherword]
                    for otherindx, otherword in enumerate(otherwords) ):
                found.append(txt)
    return found


finvindex = {word:set((txt, wrdindx)
                      for txt, wrds in texts.items()
                      for wrdindx in (i for i,w in enumerate(wrds) if word==w)
                      if word in wrds)
             for word in words}
print('\nFull Inverted Index')
pp({k:sorted(v) for k,v in finvindex.items()})

print('\nTerm Search on full inverted index for: ' + repr(terms))
pp(sorted(termsearch(terms)))

phrase = '"what is it"'
print('\nPhrase Search for: ' + phrase)
print(phrasesearch(phrase))

# Show multiple match capability
phrase = '"it is"'
print('\nPhrase Search for: ' + phrase)
ans = phrasesearch(phrase)
print(ans)
ans = Counter(ans)
print('  The phrase is found most commonly in text: ' + repr(ans.most_common(1)[0][0]))