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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 _read_data(self, dataset, format=None):
 """Reads a data file and returns and iterable that can be used as testing or training data."""

        # Attempt to detect file format if "format" isn't specified
        if not format:
            format_class = formats.detect(dataset)
        else:
            if format not in formats.AVAILABLE.keys():
                raise ValueError("'{0}' format not supported.".format(format))
            format_class = formats.AVAILABLE[format]
        return format_class(dataset).to_iterable()