Using a normal function f(x) in python

Question

I want to use a function f(x) in python. Something like ax^2 + bx + c (polynomials). I want to do that using a for loop and a list. This is what I have so far:

def f(a,x):
    for i in range (0, len(a)):
        i = ([a]*x**i)
    print (i)

for example: when I fill in f([5,2,3],5) I have to get: 3*5^0 + 2*5^1 + 5*5^2. Does somebody know how I can change my code so the output will be the result of that polynomial?

Answer 1

use a generator expression with enumerate

>>> sum(data*x**index for index, data in enumerate(reversed(a)))
138

You can use this comprehension in you func like this :

def f(a,x):
    print(sum(data*x**index for index, data in enumerate(reversed(a))))    
>>> f([5,2,3],5)    
138

EDITED : More optimized version suggested by @Paul Panzer

Answer 2

Your code is almost correct. You just need to add a running sum, and you need to select individual numbers from a

 def f(a,x):
     running = 0
     for i in range (0, len(a)):
         running += a[-1-i]*x**i
     return running