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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 checkpoint(self):
 """Dumps current samples to the checkpoint file."""

        # thin and write new samples
        for fn in [self.checkpoint_file, self.backup_file]:
            with self.io(fn, "a") as fp:
                # write the current number of iterations
                fp.write_niterations(self.niterations)
                thin_interval = self.get_thin_interval()
                # thin samples on disk if it changed
                if thin_interval > 1:
                    # if this is the first time writing, set the file's
                    # thinned_by
                    if fp.last_iteration() == 0:
                        fp.thinned_by = thin_interval
                    else:
                        # check if we need to thin the current samples on disk
                        thin_by = thin_interval // fp.thinned_by
                        if thin_by > 1:
                            logging.info("Thinning samples in %s by a factor "
                                         "of %i", fn, int(thin_by))
                            fp.thin(thin_by)
                fp_lastiter = fp.last_iteration()
            logging.info("Writing samples to %s with thin interval %i", fn,
                         thin_interval)
            self.write_results(fn)
        # see if we had anything to write after thinning; if not, don't try
        # to compute anything
        with self.io(self.checkpoint_file, "r") as fp:
            nsamples_written = fp.last_iteration() - fp_lastiter
        if nsamples_written == 0:
            logging.info("No samples written due to thinning")
        else:
            # check for burn in, compute the acls
            self.acls = None
            if self.burn_in is not None:
                logging.info("Updating burn in")
                self.burn_in.evaluate(self.checkpoint_file)
                burn_in_index = self.burn_in.burn_in_index
                logging.info("Is burned in: %r", self.burn_in.is_burned_in)
                if self.burn_in.is_burned_in:
                    logging.info("Burn-in iteration: %i",
                                 int(self.burn_in.burn_in_iteration))
            else:
                burn_in_index = 0
            # Compute acls; the burn_in test may have calculated an acl and
            # saved it, in which case we don't need to do it again.
            if self.acls is None:
                logging.info("Computing acls")
                self.acls = self.compute_acl(self.checkpoint_file,
                                             start_index=burn_in_index)
            logging.info("ACT: %s", str(numpy.array(self.acts.values()).max()))
            # write
            for fn in [self.checkpoint_file, self.backup_file]:
                with self.io(fn, "a") as fp:
                    if self.burn_in is not None:
                        fp.write_burn_in(self.burn_in)
                    if self.acls is not None:
                        fp.write_acls(self.acls)
                    # write effective number of samples
                    fp.write_effective_nsamples(self.effective_nsamples)
        # check validity
        logging.info("Validating checkpoint and backup files")
        checkpoint_valid = validate_checkpoint_files(
            self.checkpoint_file, self.backup_file)
        if not checkpoint_valid:
            raise IOError("error writing to checkpoint file")
        elif self.checkpoint_signal:
            # kill myself with the specified signal
            logging.info("Exiting with SIG{}".format(self.checkpoint_signal))
            kill_cmd="os.kill(os.getpid(), signal.SIG{})".format(
                self.checkpoint_signal)
            exec(kill_cmd)
        # clear the in-memory chain to save memory
        logging.info("Clearing samples from memory")
        self.clear_samples()