我应该在python函数/方法上做多少输入验证？

def add(x, y):
    if not isinstance(x, int) or not isinstance(y, int):
        raise TypeError("x and y must be integers")
    return x + y

def percent(value):
    assert 0 <= value <= 1, "value must be between 0 and 1"
    return value * 100

def reverse(string):
    assert string, "string cannot be empty"
    return string[::-1]

import re

def parse_date(date_string):
    pattern = r"^\d{4}-\d{2}-\d{2}$"
    if not re.match(pattern, date_string):
        raise ValueError("date_string must be in the format YYYY-MM-DD")
    return date_string