Can't call class function in python (TypeError: object() takes no parameters)

Question

I have a class:

 class MATRIX:

     # convenience function
     def getDimensions(self,M):
         r = len(M)
         c = len(M[0])
         return r,c

     def add(self,M1,M2):
         res = []
         r1,c1 = self.getDimensions(M1)
         r2,c2 = self.getDimensions(M2)
         if (r1 != r2) or (c1 != c2):
             print("dimensions not the same")
             return res

         for i in range(len(M1)):
             row=[]
             for j in range(len(M1[i])):
                 element=M1[i][j] + M2[i][j]
                 row.append(element)
             res.append(row)

    return res

Simple class, saves no state, just has a function which adds two matrices. I am a beginner at OOP in Python, so, unless I am wrong, all class functions must begin with a self parameter.

The function is meant to be called like:

 Z = MATRIX.add(X,Y)

Where X and Y are matrices

When I try to do this, I get the following error:

 Traceback (most recent call last):
   File "temp.py", line 82, in <module>
Z = MATRIX(X,Y)
 TypeError: object() takes no parameters

In this instance:

 X = [[1,1,1], [2,2,2], [3,3,3]]
 Y = [[4,4,4], [5,5,5], [6,6,6]]

Why is this error showing up? How can I fix it?

If this saves no state there is no point making it a class in Python. — Daniel Roseman
– Daniel Roseman, Commented Mar 1, 2018 at 21:00
Add a constructor that takes parameters, if you want to call a constructor MATRIX(X,Y) with parameters.. or fix the incorrect call. — user2864740
– user2864740, Commented Mar 1, 2018 at 21:01
You say you are doing Z = MATRIX.add(X, Y) but the error says Z = MATRIX(X, Y). Which is it? — internet_user
– internet_user, Commented Mar 1, 2018 at 21:02
Note that the line in the error message does not occur in the code you have posted. — Daniel Roseman
– Daniel Roseman, Commented Mar 1, 2018 at 21:02

DBedrenko · Accepted Answer · 2018-03-01 21:10:15Z

4

You need to instantiate the class MATRIX like so, before you can use its instance methods:

m = MATRIX()
z = m.add(X, Y)

But if there is no instance data, then there is not much point in having instance methods. In this case you can make the methods static, and not have to instantiate the class to make use of its methods:

class MATRIX:

    # Note that `self` parameter is removed, as it's no longer an
    # instance method.
    @staticmethod
    def add(M1,M2):
         return M1 + M2

z = MATRIX.add(X, Y)

edited Mar 1, 2018 at 21:10

answered Mar 1, 2018 at 21:04

DBedrenko

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1 Comment

DBedrenko Over a year ago

Thanks @JL-HN for the edit suggestions, unfortunately I was too late to see it, but I incorporated the changes.

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