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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def all_synsets(pos=None):
 """Return all the synsets which have the provided pos. Notes ----- Returns thousands or tens of thousands of synsets - first time will take significant time. Useful for initializing synsets as each returned synset is also stored in a global dictionary for fast retrieval the next time. Parameters pos : str Part-of-speech of the sought synsets. Sensible alternatives are wn.ADJ, wn.ADV, wn.VERB, wn.NOUN and `*`. If pos == `*`, all the synsets are retrieved and initialized for fast retrieval the next time. Returns ------- list of Synsets Lists the Synsets which have `pos` as part-of-speech. Empty list, if `pos` not in [wn.ADJ, wn.ADV, wn.VERB, wn.NOUN, `*`]. """

    def _get_unique_synset_idxes(pos):
        idxes = []

        with codecs.open(_LIT_POS_FILE,'rb', 'utf-8') as fin:
            if pos == None:
                for line in fin:
                  split_line = line.strip().split(':')
                  idxes.extend([int(x) for x in split_line[2].split()])
            else:
                for line in fin:
                    split_line = line.strip().split(':')
                    if split_line[1] == pos:
                        idxes.extend([int(x) for x in split_line[2].split()])
        idxes = list(set(idxes))
        idxes.sort()
        return idxes

    if pos in LOADED_POS:
        return [SYNSETS_DICT[idx] for lemma in LEM_POS_2_SS_IDX for idx in LEM_POS_2_SS_IDX[lemma][pos]]
    else:
        synset_idxes = _get_unique_synset_idxes(pos)

        if len(synset_idxes) == 0:
            return []

        stored_synsets = [SYNSETS_DICT[synset_idxes[i]] for i in range(len(synset_idxes)) if synset_idxes[i] in SYNSETS_DICT]
        unstored_synset_idxes = [synset_idxes[i] for i in range(len(synset_idxes)) if synset_idxes[i] not in SYNSETS_DICT]
        
        synset_offsets = _get_synset_offsets(unstored_synset_idxes)
        synsets = _get_synsets(synset_offsets)

        for synset in synsets:
            for variant in synset.get_variants():
                LEM_POS_2_SS_IDX[variant.literal][synset.pos].append(synset.id)

        LOADED_POS.add(pos)

        return stored_synsets + synsets