我得到一个 NameError 'matrix_add' is not defined：尝试重载 __add__ 函数时

Question

我正在为一个编程类做作业，我需要重载标准运算符（+、*、-）并让它们与 Matrix 类对象一起工作。我认为我做得很好，但是 Python 不断吐出一个名称错误，我不知道为什么，因为函数已定义。

我已经尝试了很多东西，但我仍然不断地回到我的原始代码（如下）。请帮忙

class Matrix:
    """A Class Matrix which can implement addition, subtraction and multiplication 
    of two matrices; scalar multiplication; and inversion, transposition and
    determinant of the matrix itself"""

    def __init__(self, a):
        """Constructor for the Class Matrix"""
        #what if you only want to work with one matrix
        self.a = a


    def __add__(self, b):

        return matrix_add(self.a, b)

    def matrix_add(self, a, b):
        """
        Add two matrices.

        Matrices are represented as nested lists, saved row-major.

        >>> matrix_add([[1,1],[2,2]], [[0,-2],[3,9]])
        [[1, -1], [5, 11]]
        >>> matrix_add([[2,3],[5,7]], [[11,13],[17,19]])
        [[13, 16], [22, 26]]
        >>> matrix_add([[2,3,4],[5,7,4]], [[11,13,1],[17,19,1]])
        [[13, 16, 5], [22, 26, 5]]
        >>> matrix_add([[1,2],[3,4]],[[1,2]])
        Traceback (most recent call last):
        ...
        MatrixException: matrices must have equal dimensions
        """
        rows = len(a)     # number of rows
        cols = len(a[0])  # number of cols

        if rows != len(b) or cols != len(b[0]):
            raise MatrixException("matrices must have equal dimensions")

        return [[a[i][j] + b[i][j] for j in range(cols)] for i in range(rows)]

我使用以下方式调用它：

A = Matrix([[1, 2, 3], [1, 2, 3], [1, 2, 3]])
B = Matrix([[2, 3, 4], [2, 3, 4], [2, 3, 4]])

我收到此错误消息：

----------------------------------------------------------------------
NameError                        Traceback (most recent call last)
<ipython-input-113-74230a6e5fb2> in <module>()
----> 1 C = A + B

<ipython-input-110-e27f8d893b4d> in __add__(self, b)
     22     def __add__(self, b):
     23 
---> 24         return matrix_add(self.a, b)
     25 


NameError: name 'matrix_add' is not defined

Answer 1

只需将列表直接发送到矩阵

class Matrix:
        """A Class Matrix which can implement addition, subtraction and multiplication 
        of two matrices; scalar multiplication; and inversion, transposition and
        determinant of the matrix itself"""

        def __init__(self, a):
            """Constructor for the Class Matrix"""
            #what if you only want to work with one matrix
            self.a = a


        def __add__(self, b):

            return self.matrix_add(self.a, b.a)

        def matrix_add(self, a, b):
            """
            Add two matrices.

            Matrices are represented as nested lists, saved row-major.

            >>> matrix_add([[1,1],[2,2]], [[0,-2],[3,9]])
            [[1, -1], [5, 11]]
            >>> matrix_add([[2,3],[5,7]], [[11,13],[17,19]])
            [[13, 16], [22, 26]]
            >>> matrix_add([[2,3,4],[5,7,4]], [[11,13,1],[17,19,1]])
            [[13, 16, 5], [22, 26, 5]]
            >>> matrix_add([[1,2],[3,4]],[[1,2]])
            Traceback (most recent call last):
            ...
            MatrixException: matrices must have equal dimensions
            """
            rows = len(a)     # number of rows
            cols = len(a[0])  # number of cols

            if rows != len(b) or cols != len(b[0]):
                raise MatrixException("matrices must have equal dimensions")

            return [[a[i][j] + b[i][j] for j in range(cols)] for i in range(rows)]

    A = Matrix([[1, 2, 3], [1, 2, 3], [1, 2, 3]])
    B = Matrix([[2, 3, 4], [2, 3, 4], [2, 3, 4]])
    print(A+B)

Answer 2

您必须缩进除第一行以外的所有行，在 matrix_add 函数调用之前加上 self（如 @Arman 所说）和 implement a __len__(self) function：

class Matrix:
    """A Class Matrix which can implement addition, subtraction and multiplication 
    of two matrices; scalar multiplication; and inversion, transposition and
    determinant of the matrix itself"""

    def __init__(self, a):
        """Constructor for the Class Matrix"""
        #what if you only want to work with one matrix
        self.a = a


    def __add__(self, b):

        return self.matrix_add(self.a, b)

    def __len__(self):
        # TODO: FILL THIS IN
        pass

    def matrix_add(self, a, b):
        """
        Add two matrices.

        Matrices are represented as nested lists, saved row-major.

        >>> matrix_add([[1,1],[2,2]], [[0,-2],[3,9]])
        [[1, -1], [5, 11]]
        >>> matrix_add([[2,3],[5,7]], [[11,13],[17,19]])
        [[13, 16], [22, 26]]
        >>> matrix_add([[2,3,4],[5,7,4]], [[11,13,1],[17,19,1]])
        [[13, 16, 5], [22, 26, 5]]
        >>> matrix_add([[1,2],[3,4]],[[1,2]])
        Traceback (most recent call last):
        ...
        MatrixException: matrices must have equal dimensions
        """
        rows = len(a)     # number of rows
        cols = len(a[0])  # number of cols

        if rows != len(b) or cols != len(b[0]):
            raise MatrixException("matrices must have equal dimensions")

        return [[a[i][j] + b[i][j] for j in range(cols)] for i in range(rows)]

在此之后，您还会遇到另一个错误，要求您必须实现另一个功能。谷歌一下，祝你好运;-)