Help trying to write a function

[Gribouillis]

Don't use the import * construct, it leads to inconsistencies in the current namespace. Use this for example

import math
import sympy as sy
import pylab
 
xo,yo,zo=sy.symbols('xo yo zo', real=True)
xo=sy.log(yo)
 
dyo1=sy.diff(xo, yo)
print ("dxo/dyo="),dyo1

Then you're sure that the log() function from module sympy is used and not the log() function from the numpy module imported in pylab.