Python - Help defining a class with a variable number of attributes depending on the argument

Question

Define a Python class Polynomial which provides methods for performing algebraic operations on polynomials. Your class should behave as described in the following sample transcript:

>>> p1 = Polynomial([1, 2, 3])
>>> p1
1.000 z**2 + 2.000 z + 3.000
>>> p2 = Polynomial([100, 200])
>>> p1.add(p2)
1.000 z**2 + 102.000 z + 203.000
>>> p1 + p2
1.000 z**2 + 102.000 z + 203.000
>>> p1(1)
6.0
>>> p1(-1)
2.0
>>> (p1 + p2)(10)
1323.0
>>> p1.mul(p1)
1.000 z**4 + 4.000 z**3 + 10.000 z**2 + 12.000 z + 9.000
>>> p1 * p1
1.000 z**4 + 4.000 z**3 + 10.000 z**2 + 12.000 z + 9.000
>>> p1 * p2 + p1
100.000 z**3 + 401.000 z**2 + 702.000 z + 603.000
>>> p1.roots()
[(-1+1.4142135623730947j), (-1-1.4142135623730947j)]
>>> p2.roots()
[-2.0]
>>> p3 = Polynomial([3, 2, -1])
>>> p3.roots()
[-1.0, 0.33333333333333331]
>>> (p1 * p1).roots()
Order too high to solve for roots.

How would you go about designing this function so it can take polynomials of different grades. I'm really lost.

Thanks.

Why do you need a variable number of attributes? Use a single attribute containing a list. — Barmar, Mar 02 '16 at 23:28
http://stackoverflow.com/questions/1535327/python-how-to-print-a-class-or-objects-of-class-using-print — Barmar, Mar 02 '16 at 23:36
Define `__repr__` and `__str__` methods in your class that loop through the list and print the values. — Barmar, Mar 02 '16 at 23:37

YBathia · Answer 1 · 2016-03-03T04:23:58.640

3

You can create a class with variable number of attributes:

class Var:
    def __init__(self,**kwargs):
        for attr in kwargs.keys():
            self.__dict__[attr] = kwargs[attr]




v = Var(name="Sam",age=22)
print(v.__dict__)
print(v.name)
print(v.age)

Output:

{'age': 22, 'name': 'Sam'}
Sam
22

But if you want to pass a list as an argument and assign each member of the list to an attribute inside the class, whose name is going to be a letter, ascending in every attribute, you can do something like:

class Var:
    def __init__(self,*args):
        keyVal = 97
        for attr in args:
            self.__dict__[chr(keyVal)] = attr
            keyVal+=1




v1 = Var(1,2,3)
print('Attributes of v1',v1.__dict__)
myList = [4,5]
v2 = Var(*myList)
print("attributes of v2",v2.__dict__)

Output:

('Attributes of v1', {'a': 1, 'c': 3, 'b': 2})
('attributes of v2', {'a': 4, 'b': 5})

edited Mar 03 '16 at 04:23

answered Mar 02 '16 at 23:37

YBathia

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I'm sorry i do not know what __dict__ or kwargs means – Andrés Mar 02 '16 at 23:47
@AndrésRivero: kwargs means keyword arguments , in the form of name="Sam",age=22 . These kwargs can be accessed inside a function just like a dictionary, the dictionary in this case being kwargs. A simple explanation of python dictionary is given here: http://www.tutorialspoint.com/python/python_dictionary.htm – YBathia Mar 02 '16 at 23:49
Ok. But what if I want to pass a list as an argument. And assign each member of the list to an attribute inside the class, whose name is going to be a letter, ascending in every attribute, as in: `self.a = 3`, `self.b = 4` etc. – Andrés Mar 03 '16 at 01:13
@AndrésRivero: Added more content to my solution, this should answer your question – YBathia Mar 03 '16 at 04:24

Python - Help defining a class with a variable number of attributes depending on the argument

1 Answers1