Returns a list of the type choices

def get_digest_keys(self):
        """Returns a list of the type choices"""

        digest_keys = []
        for col in xrange(self.GetNumberCols()):
            digest_key = self.GetCellValue(self.has_header, col)
            if digest_key == "":
                digest_key = self.digest_types.keys()[0]
            digest_keys.append(digest_key)

        return digest_keys