def __init__(self, const=False, optional=False):
        """
        const (bool):
            True if the InputType has to be constant / materialized at compile time.
            Const InputType is semantically equivalent to attribute. By
            default False. Read-only.

        optional (bool):
            True to allow user not to specify this input and rely on default
            values (defined in default_inputs).

        Note: _InputType should not be directly instantiated. Only its subclasses may
        be instantiated.
        """
        self.const = const
        self.optional = optional

        const (bool):
            True if the InputType has to be constant / materialized at compile time.
            Const InputType is semantically equivalent to attribute. By
            default False. Read-only.

        optional (bool):
            True to allow user not to specify this input and rely on default
            values (defined in default_inputs).

        Note: _InputType should not be directly instantiated. Only its subclasses may
        be instantiated.
        
coremltools/converters/mil/mil/input_type.py