class BaseStructure(ctypes.Structure):

    def __init__(self, **kwargs):
        """
        Ctypes.Structure with integrated default values.
        :param kwargs: values different to defaults
        :type kwargs: dict
        """
values = type(self)._defaults_.copy()
for key, val in list(kwargs.items()):
    values[key] = val
super().__init__(**values)


class YourStructure(BaseStructure):
    _fields_ = [('param1', ctypes.c_uint32), ('param2', ctypes.c_uint32), (
        'param3', ctypes.c_int32)]
_defaults_ = {'param1': 42, 'param3': -23}
Значения по умолчанию в структуре ctypes