Question

I’m trying to pass a numpy matrix to an object method but I keep getting TypeError: test_obj() takes exactly 1 argument (2 given)

I think the matrix object is not getting interpreted properly as a matrix object, however when the same code is run as simple function it works fine. How can I get my object method to work like the simple function?

code:

from numpy import *

class Tester(object):
    def test_obj(x):
        print 'test obj:', type(x)

    def test_fun(x):
        print 'test fun:', type(x)

X = matrix('5.0 7.0')

test_fun(X)

tester = Tester()
tester.test_obj(X)

output:

test fun: <class 'numpy.matrixlib.defmatrix.matrix'>
Traceback (most recent call last):
  File "/home/fornarim/test_matrix.py", line 22, in <module>
    tester.test_obj(X)
TypeError: test_obj() takes exactly 1 argument (2 given)

Answer 1

All objects’ methods take an implicit self argument, so your method test_fun must be

def test_fun(self,arg):

Unlike in Java, in Python you must refer back to the object.

As mentioned below, also possible is using the @staticmethod decorator to indicate that the function does not need a reference to the object.

@staticmethod
def test_fun(arg):