Imagine your friend had a Python function that created that expression. Let's call it create_symbolic_expression() and put it into a file sympy_demo.py. My demonstration is likely to be more simple than the one you have in mind.
sympy_demo.py also contains a function that lambdify's this symbolic expression..that is, it creates a Python function in the variables x,y and z.
from sympy import lambdify
from sympy.abc import x,y,z
This is a proxy for whatever code your friend has written but I'll keep it simple for this demo.
expr = x+y+z
We can now go to MATLAB, ensure sympy_demo.py is on your path and do
expr = create_symbolic_expression()
myfunc = lambdify_expression(expr)
We can now evaluate myfunc with numeric inputs