I get a NameError 'matrix_add' is not define: when trying to overload the add function

Question

I am doing an assignment for a programming class where I am required to overload the standard operators (+, *, -) and have them work with Matrix class objects. I think I am doing it properly but Python keeps spitting out a name error and I have no Idea why, since the function is defined.

I have tried many things, but I still keep coming back to my original code (below). Please help

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)]

I'm calling it using the following:

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

And i get this error message:

----------------------------------------------------------------------
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

`self.matrix_add` instead `matrix_add` in `__add__` function. — ᴀʀᴍᴀɴ, Jan 19 '17 at 10:36
And even when i write: return self.matrix_add(a, b) I get another error message object of type Matrix has no len() — rdmtinez, Jan 19 '17 at 10:39
You don't need pass `a` as a parameter to `matirx_add` , just use it as class attribute , `a.self` instead `a` — ᴀʀᴍᴀɴ, Jan 19 '17 at 10:42
@RicardoMartinez: sure, there can be *other* errors too, but the error posted *in your question* is caused by the lack of using `self`. — Martijn Pieters, Jan 19 '17 at 10:43
@RicardoMartinez: you are calling `len()` on a `Matrix` instance. You didn't provide a `__len__` method, so that *also* breaks. — Martijn Pieters, Jan 19 '17 at 10:44
@Arman, that solved that issue, thanks a lot, but now I can't seem to get the len() function working properly — rdmtinez, Jan 19 '17 at 10:45
see Martijin comments , as he said there is no `__len__` method for `Matrix` instance. — ᴀʀᴍᴀɴ, Jan 19 '17 at 10:46
I get that, but I don't see why it matters, shouldn't it just use the regular len to find the length of a matrix, or how do i make it so that len() is called on the matrix that is the object, rather than the object itself? — rdmtinez, Jan 19 '17 at 10:48

score 0 · Answer 1 · answered Jan 19 '17 at 10:49

You have to indent all lines except the first, precede the matrix_add function call with self (as @Arman said) and 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)]

After this, you are also going to get another error, asking for yet another function which you have to implement. Google it, and good luck ;-)

score 0 · Accepted Answer · answered Jan 19 '17 at 10:50

just send the list directly to the matrix

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)

we send the list a of object b – Smart Manoj Jan 19 '17 at 10:53 — Smart Manoj, Jan 19 '17 at 10:53

I get a NameError 'matrix_add' is not define: when trying to overload the __add__ function

2 Answers2

I get a NameError 'matrix_add' is not define: when trying to overload the add function