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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 _output_dir( self, ext, is_instance=False, interpolatable=False, autohinted=False, is_variable=False, ):
 """Generate an output directory. Args: ext: extension string. is_instance: The output is instance font or not. interpolatable: The output is interpolatable or not. autohinted: The output is autohinted or not. is_variable: The output is variable font or not. Return: output directory string. """


        assert not (is_variable and any([is_instance, interpolatable]))
        # FIXME? Use user configurable destination folders.
        if is_variable:
            dir_prefix = "variable_"
        elif is_instance:
            dir_prefix = "instance_"
        else:
            dir_prefix = "master_"
        dir_suffix = "_interpolatable" if interpolatable else ""
        output_dir = dir_prefix + ext + dir_suffix
        if autohinted:
            output_dir = os.path.join("autohinted", output_dir)
        return output_dir