Iterating over a two lists of integers in python? -

i'm coding function produce , being expression.

given 2 lists: xs , ys , x wrote algorithm below:

#!/usr/bin/env python #coding: utf8  sympy import * numpy import * import json  l = {} x = symbol('x') expresion = '' def lagrange(xs, ys, x):      k in len(xs):          if k != 0 or k != len(xs)-1: #si no es el primero o el último término de la sumatoria             expresion = expresion + '+' + ys[k] + '*'         elif k==0:             expresion = expresion + ys[k] + '*'         in len(xs):             if k==i:                 continue # si i==k saltamos esta iteración para eliminar división sobre cero             expresion = expresion + '(' + '(' + x + '-' + xs[i] +' )' + '/' + '(' + xs[k] + '-' + xs[i] + ')' +')'     print simpify(expresion) 

when ran:

#!/usr/bin/env python #coding: utf8   lagrange import *  lagrange([0,1,2,4],[-1,0,7,4,63],3) 

i got:

[......]line 12, in lagrange     k in len(xs): typeerror: 'int' object not iterable [finished in 0.5s exit code 1] 

so how should iterate on xs , ys elements , include condition if i=k continue on loop?

for k in range(len(xs)) 

will give possible indicies in xs.

len(xs) returns int, not iterable. want same i loop.