input: Write a function to evaluate a mathematical expression given as a string.
  assert eval_expr("2 + (3 * 5)") == 17
  assert eval_expr("10 / 2 - 3") == 2.0
  assert eval_expr("4 * (2 + 3)") == 20
output: def eval_expr(expression: str) -> float:
      return eval(expression)