跟蹤陣列上的額外屬性

class MySubClass(np.ndarray):
    def __new__(cls, input_array, info=None):
        obj = np.asarray(input_array).view(cls)
        obj.info = info
        return obj

    def __array_finalize__(self, obj):
        # handles MySubClass(...)
        if obj is None:
            pass

        # handles my_subclass[...] or my_subclass.view(MySubClass) or ufunc output
        elif isinstance(obj, MySubClass):
            self.info = obj.info

        # handles my_arr.view(MySubClass)
        else:
            self.info = None

    def __array_prepare__(self, out_arr, context=None):
        # called before a ufunc runs
        if context is not None:
            func, args, which_return_val = context

        return super().__array_prepare__(out_arr, context)

    def __array_wrap__(self, out_arr, context=None):
        # called after a ufunc runs
        if context is not None:
            func, args, which_return_val = context

        return super().__array_wrap__(out_arr, context)

對於 context 元組，func 是一個 ufunc 物件，如 np.add，args 是 tuple，which_return_val 是一個整數，指定正在處理 ufunc 的返回值