simplify math expressions with sympy

simplify.py

import sympy
import readline # allow arrow keys while typing inputs

while True:
    expression = input("expression: ")
    unknowns = input("unknowns comma delimited: ")

    exec_str = f"{unknowns} = sympy.symbols(\"{unknowns}\")"
    print(f"> {exec_str}")
    exec(exec_str)

    exec_str = f"expr = {expression}"
    print(f"> {exec_str}")
    exec(exec_str)

    print(f"> expr.simplify()")
    print(expr.simplify())
    print()

expression: (s+0.4)*(s**2-0.36*s+0.16)*(s+9)+25*(s+0.03)*(0.71)*(s+1)
unknowns comma delimited: s
> s = sympy.symbols("s")
> expr = (s+0.4)*(s**2-0.36*s+0.16)*(s+9)+25*(s+0.03)*(0.71)*(s+1)
> expr.simplify()
1.0*s**4 + 9.04*s**3 + 18.126*s**2 + 18.4905*s + 1.1085

user input was on the first 2 lines, nowhere else