在 function 内的全局表达式中替换一个局部值

Question

I want to substitute some parameters inside the function (i) without creating additional parameters of the function f(parameters), (ii) without changing variables globally. The problem is that one variable is defined outside the function and I would like to keep it this way (z can be potentially a result of many other preceding cells).

import sympy
x_hh=sympy.Symbol("x_hh") 
z=x_hh+2;

def v():
    x_hh=2;
    a=1;
    utility = a*z
    return utility
display(v())

As the output I have x_hh+2 , but I want to have 4 .

Answer 1

Your code will be interpreted from up to down. So z=x_hh+2; will only be called once at the beginning.

you could simply create a new variable inside the funciton:

import sympy
x_hh=sympy.Symbol("x_hh") 
z=x_hh+2

def v():
    x_hh=2; #the value of x_hh was changed here
    new_var = x_hh+2 # this variable will be up-to-date and won't affect z
    a=1;
    utility = a*new_var #we use the new variable instead of z
    return utility
display(v())