Python class Polynomials won't work, like I expect it to work

Question

For exercise we should create a class Polynomials, which stores the coefficients of a Polynomial of one variable (1 dimensional), implementing the print function, multiplication, sum and subtraction of two polynomials, the evaluation in one point as a functor and two methods implementing the derivative and the integral of the polynomial(integration constants set to zero).

I tried to create a Class Polynomials, where I can create a Polynomial with n coefficients and implemented the methods.

When I don't use an extra class and create Polynomials like p1 = np.poly1d([...]), the code just works fine. But as soon as I create the class Polynomials and use my __init__ function, the code shows several errors, when calling other methods.

Whether it's Key errors or Polynomials object has no attribute '_variable'

My Code:

import numpy as np

class Polynomials (np.poly1d):
    def __init__(self, coefficients):
        self.name = np.poly1d(coefficients)

    def Coefficients(self):
        return self.c

    def evaluation(self, x):
        return self(x)

    def mul(self, a):
        return np.polymul(self, a)

    def sum(self, a):
        return np.polyadd(self, a)

    def subtraction(self, a):
        return np.polysub(self, a)

    def __str__(self):
        return str(self.name)

def differentiate(self):
    return np.polyder(self)

def integrate(self):
    return np.polyint(self)


a= Polynomials([2,5,7,8])
b = Polynomials([3,5,7,1])
print (a)
print(b)
#print(a(10))
c = a.mul(b)
#print(c)

Error code looks like:

line 14, in mul
    return np.polymul(self, a)
  File "<__array_function__ internals>", line 6, in polymul
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/numpy/lib/polynomial.py", line 904, in polymul
    a1, a2 = poly1d(a1), poly1d(a2)
  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-               packages/numpy/lib/polynomial.py", line 1155, in __init__
    self._variable = c_or_r._variable
   AttributeError: 'Polynomials' object has no attribute '_variable'

I already tried to test, what object I really create there with print(isinstance(a, np.poly1d)), which shows true, when I create the polynomial within the new class AND when I create it without the Class.

So, why can I perform all operations with the created polynomial, when I create it without the class and can't perform it, when I create it in the class? Where am I lost?

Answer 1

Try this:

class Polynomials (np.poly1d):
    def __init__(self, coefficients):
        super().__init__(coefficients)
        self.name = np.poly1d(coefficients)

    # ...

Otherwise you never run any of the poly1d initialisation procedures.