Python中如何实现数据校验并自定义validator轮子

在Python里做数据校验，我一般用Pydantic，但自己造轮子也简单。核心就是写个类，用描述符（descriptor）或者__setattr__来拦截赋值操作。

下面这个Validator类就是个基础轮子。它用__init__定义字段和校验规则，__setattr__在赋值时触发校验。validate方法里你可以写任何校验逻辑，比如类型检查、范围判断或者自定义函数。校验失败就抛个ValueError。

class Validator:
    def __init__(self):
        self._validators = {}
        self._data = {}

    def add_field(self, name, validator_func):
        """添加字段和对应的校验函数"""
        self._validators[name] = validator_func
        self._data[name] = None

    def __setattr__(self, name, value):
        if name.startswith('_'):
            super().__setattr__(name, value)
        else:
            if name in self._validators:
                validator = self._validators[name]
                if not validator(value):
                    raise ValueError(f"Validation failed for field '{name}' with value {value}")
                self._data[name] = value
            else:
                raise AttributeError(f"No validator defined for field '{name}'")

    def __getattr__(self, name):
        if name in self._data:
            return self._data[name]
        raise AttributeError(f"No such field: '{name}'")

# 使用示例
def is_positive(x):
    return isinstance(x, (int, float)) and x > 0

def is_non_empty_string(s):
    return isinstance(s, str) and len(s) > 0

# 创建实例并添加字段
obj = Validator()
obj.add_field('age', is_positive)
obj.add_field('name', is_non_empty_string)

# 测试赋值
try:
    obj.age = 25  # 通过
    print(f"Age: {obj.age}")
    obj.name = "Alice"  # 通过
    print(f"Name: {obj.name}")
    obj.age = -5  # 触发 ValueError
except ValueError as e:
    print(e)

想更Pythonic的话，可以用描述符。下面这个ValidatedAttribute描述符把校验逻辑封装在__set__里，用起来更干净。

class ValidatedAttribute:
    def __init__(self, validator):
        self.validator = validator
        self.attr_name = None

    def __set_name__(self, owner, name):
        self.attr_name = name

    def __get__(self, obj, objtype=None):
        if obj is None:
            return self
        return obj.__dict__.get(self.attr_name)

    def __set__(self, obj, value):
        if not self.validator(value):
            raise ValueError(f"Invalid value {value} for {self.attr_name}")
        obj.__dict__[self.attr_name] = value

# 使用描述符的类
class Person:
    age = ValidatedAttribute(is_positive)
    name = ValidatedAttribute(is_non_empty_string)

    def __init__(self, name, age):
        self.name = name
        self.age = age

# 测试
try:
    p = Person("Bob", 30)
    print(f"Person: {p.name}, {p.age}")
    p.age = -10  # 触发 ValueError
except ValueError as e:
    print(e)

简单需求自己写，复杂项目直接用Pydantic。

原来文档里有…无视我😂

GJ!