keras/src/dtype_policies/dtype_policy.py/QuantizedDTypePolicy/__init__
class QuantizedDTypePolicy:    def __init__(self, mode, source_name=None):
        # Use the global dtype policy if `source_name` is not specified
        if source_name is None:
            source_name = dtype_policy().name
        name = f"{mode}_from_{source_name}"
        self._compute_dtype, self._variable_dtype = self._parse_name(
            source_name
        )
        self._check_quantization_mode(mode, self._compute_dtype)

        self._name = name
        self._source_name = source_name
        self._quantization_mode = mode