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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 train(self, nerdocs, mode_filename):
 """Train a CRF model using given documents. Parameters nerdocs: list of estnltk.estner.ner.Document. The documents for model training. mode_filename: str The fielname where to save the model. """


        trainer = pycrfsuite.Trainer(algorithm=self.algorithm,
                                     params={'c2': self.c2},
                                     verbose=self.verbose)

        for doc in nerdocs:
            for snt in doc.sentences:
                xseq = [t.feature_list() for t in snt]
                yseq = [t.label for t in snt]
                trainer.append(xseq, yseq)

        trainer.train(mode_filename)