Should I use a class? (Python)

Question

I'm trying to write a small Python module which contain some mathematical functions. For example, it might contain a function like:

def quad(x, a, b, c):
    return a*x**2 + b*x + c

As you may notice it contains several parameters (viz. a, b, c) apart from the variable x. Now if I were to put this in a file and simply import it, the end user would have to always call the function with the parameters in addition to the variable. Because of this I was thinking of creating a class such as this:

class quad:                                    
    def __init__(self, a, b, c):               
        self.a = a                             
        self.b = b                             
        self.c = c                             

    def eq(x):                               
        return self.a*x**2 + self.b*x + self.c 

Thus allowing the end user to use it as:

q = quad(p, q, r) 
eq = q.eq      

Is this the right way of doing things? I am terribly sorry about the title of the question, as I couldn't think of a better one!

Answer 1

That seems like a perfectly reasonable use of a class. Essentially you should consider using a class when your program involves things that can be modelled as objects with state. Here, the "state" of your polynomial is just the coefficients a, b, and c.

You can also use Python's __call__ special method to allow you to treat the class as though it were a function itself:

class quad:
    def __init__(self, a, b, c):
        self.a = a
        self.b = b
        self.c = c

    def __call__(x):
        return self.a * x**2 + self.b * x + self.c

q = quad(p, q, r)
q(x)

---

Yet another way of doing it, which could be slightly cleaner, would be simply to return a function with those coefficients baked into it. This is essentially an example of currying, as Tichodrama mentions:

def quad(a, b, c):
    def __quad(x):
        return a * x**2 + b * x + c

    return __quad

Or using lambda syntax:

def quad(a, b, c):
    return lambda x: a * x**2 + b * x + c

These could then be used like so:

q = quad(p, q, r)
q(x)

Answer 2

It looks like you are searching for something like currying.

Perhaps this question can help you.