Python策略模式应用

# Python 策略模式 (Strategy Pattern)
# Strategy 接口，运行时选择策略，策略注册表，验证策略
# -----------------------------------------------------------
# 策略模式定义一系列可互换的算法，使算法独立于使用它的
# 客户端。核心：策略接口 + 具体策略 + 策略上下文。
# -----------------------------------------------------------

from abc import ABC, abstractmethod
from typing import Any

# ===================== 策略接口 =====================
class ValidationStrategy(ABC):
@abstractmethod
def validate(self, data: dict) -> list[str]: ...

# ===================== 具体策略 =====================
class RequiredFieldStrategy(ValidationStrategy):
def __init__(self, fields: list[str]):
self._fields = fields
def validate(self, data: dict) -> list[str]:
return [f"{f} 为必填项" for f in self._fields
if f not in data or not data.get(f)]

class RangeStrategy(ValidationStrategy):
def __init__(self, field: str, min_v: float, max_v: float):
self._field = field; self._min = min_v; self._max = max_v
def validate(self, data: dict) -> list[str]:
v = data.get(self._field)
if v is not None:
try:
fv = float(v)
if fv < self._min or fv > self._max:
return [f"{self._field} 需在 {self._min}-{self._max}"]
except (ValueError, TypeError):
return [f"{self._field} 必须为数字"]
return []

class EmailStrategy(ValidationStrategy):
def validate(self, data: dict) -> list[str]:
email = data.get("email", "")
return ["邮箱格式无效"] if email and "@" not in email else []

class LengthStrategy(ValidationStrategy):
def __init__(self, field: str, min_l: int, max_l: int):
self._field = field; self._min = min_l; self._max = max_l
def validate(self, data: dict) -> list[str]:
val = str(data.get(self._field, ""))
if not (self._min <= len(val) <= self._max):
return [f"{self._field} 长度需 {self._min}-{self._max} 字符"]
return []

# ===================== 策略上下文 =====================
class Validator:
"""验证上下文：组合多个策略进行校验"""
def __init__(self):
self._strategies: list[ValidationStrategy] = []
def add(self, s: ValidationStrategy) -> "Validator":
self._strategies.append(s); return self
def validate(self, data: dict) -> list[str]:
errors = []
for s in self._strategies:
errors.extend(s.validate(data))
return errors

# ===================== 策略注册表 =====================
class StrategyRegistry:
"""按名称动态查找和创建策略"""
def __init__(self):
self._reg: dict[str, type[ValidationStrategy]] = {}
def register(self, n: str, s: type[ValidationStrategy]) -> None:
self._reg[n] = s
def create(self, n: str, **kw) -> ValidationStrategy:
cls = self._reg.get(n)
if cls is None:
raise ValueError(f"未知策略: {n}")
return cls(**kw)

if __name__ == "__main__":
v = Validator()
v.add(RequiredFieldStrategy(["name", "email", "age"])) \
.add(EmailStrategy()) \
.add(RangeStrategy("age", 18, 120)) \
.add(LengthStrategy("name", 2, 50))
errs = v.validate({"name": "A", "email": "bad", "age": "200"})
for e in errs:
print(f"验证失败: {e}")