user input string to function

Mon Dec 25 08:36:16 EST 2017

Hi everybody. First ad foremost, happy Christmas!
I want to let the use input a function (like x**2) and parse it after that through code (for my numeric class)
import numpy as np
import matplotlib.pyplot as plt
import scipy.linalg
from sympy.abc import o, h
import sympy
from sympy import symbols
from scitools.StringFunction import StringFunction
from sympy.plotting import plot
x = symbols('x')
def newton(x0, s, s2, tol, n = 20000):
 '''
 Näherung zur lösung einer Gleichung mit dem Newton-Verfahren
 x0 = Startwert
 f = zu lösende Funktion
 fx = Ableitung der Funktion

 '''
 def f(a):
 y = s
 return y

 def fx(a):
 y = s2
 return y

 a = x0
 k = 0

 while n > k:
 k += 1 
 b = a - f(a)/fx(a)
 print('x', k, '\n',b)

 print('Startwert -> x0', '\n', x0)
 print('Anzahl Iterationen', '\n', k)
 print('f(x~)', '\n', f(x))
 print('Näherungswert -> x~', '\n', b)

 return x0, k, f(x), x
(Please ignore all the input, they are used latter)
Now the output looks like this:
newton(2, 3*x**2, 6*x, 0.1, 2)
x 1 
 -x/2 + 2
x 2 
 -x/2 + 2
Startwert -> x0 
 2
Anzahl Iterationen 
 2
f(x~) 
 3*x**2
Näherungswert -> x~ 
 -x/2 + 2
Out[166]: (2, 2, 3*x**2, x)
I notice that the x is not converted to an integer, because of the x = symplos('x')
But I don't know how I could possibli change the code to work...
Regards
Nicco