使用python评估多项式

Question

I'm trying to create my own polynomial class. I want to make a function that can evaluate a polynomial where x is given.

So far I have this, however the answers its giving me aren't right and I cant figure out why? The polynomials are inputted using a list. For example [2, 0, 1, -7, 13] would be 2x^4+x^2-7x+13

class Polynomial:

def __init__(self, coefficients):
    self.coeffs=coefficients

def evaluate(self, x):
    sum = 0
    for i in range(len(self.coeffs)-1,0,-1):
        sum+=self.coeffs[i]*(x**i)
    return sum

Answer 1

The i value you're using isn't right for both the index and the exponent. You're actually evaluating the reversed-coefficeint polynomial, so your evaluation results for Polynomial([2,3,4]) are actually the right value for Polynomial([4,3,2]) .

Here's how I'd define evaluate :

def evaluate(self, x):
    return sum(coef * x**exp for exp, coef in enumerate(reversed(self.coeffs)))

Note that if you want your Polynomial objects to be callable (as in p1(4) in the example in your comment), you should rename your evaluate function __call__ .

Answer 2

There is an error expected an indented block for this code. To resole the error, be sure to include an indentation block:

class Polynomial:
    def __init__(self, coefficients):
        self.coeffs=coefficients

    def _call_(self, x):
    return sum(coef * x**exp for exp, coef in enumerate(reversed(self.coeffs)))