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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 _check_file_field(self, field):
 """Check that field exists and is a file field"""

        is_field = field in self.field_names
        is_file = self.__meta_metadata(field, 'field_type') == 'file'
        if not (is_field and is_file):
            msg = "'%s' is not a field or not a 'file' field" % field
            raise ValueError(msg)
        else:
            return True