[英]How to express hasattr() duck typing logic with structural pattern matching?
用于结构模式匹配的PEP 634将此功能记录为class 模式:
cls()
将执行isinstance()测试。cls(attr=variable)
测试属性是否存在并将值绑定到变量。_fields
,这是必须存在的属性。_
,如果您确实想捕获该值,请将其设置为其他变量名。您的具体示例, if hasattr(candidate, '_fields'): do_action()
,转换为:
match candidate:
case object(_fields=_):
do_action()
这显示了所有部分如何组合在一起:
from typing import NamedTuple
from dataclasses import dataclass
class Whale(NamedTuple):
name: str
num_fins: int
@dataclass
class Vehicle:
name: str
num_wheels: int
subject = Vehicle('bicycle', 2)
match subject:
case object(num_fins=n):
print(f'Found {n} fins')
case object(num_wheels=_):
print(f'Found wheeled object')
case _:
print('Unknown')
该脚本输出:
Found wheeled object
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