Как валидировать значение полученное от пользователя

if not isinstance(user_input, str):
    raise ValueError("Input must be a string")

import re
if not re.match(r'^[a-zA-Z0-9_]+$', username):
    raise ValueError("Invalid characters in username")

from email_validator import validate_email
try:
    email = validate_email(user_email).email
except Exception as e:
    print(str(e))

from pydantic import BaseModel, ValidationError

class User(BaseModel):
    name: str
    age: int

try:
    user = User(name="John", age="twenty")
except ValidationError as e:
    print(e)