自定义typing.NamedTuple [英] customizing typing.NamedTuple

问题描述

我使用 NamedTuple 来保存数据，并且我想添加一个可以被多个基于 NamedTuple 的类继承的方法.但是当我尝试使用多重继承或子类化基于 NamedTuple 的类时，它不起作用.具体来说，我试图自动为我的所有数据类提供一个方法，该方法可以查看类注释，然后基于该方法调用一些序列化代码.以下是我尝试过的一些示例:

from 输入 import NamedTuple类 Base1:def foo(self):打印(自我.__注释__)类 Test1(NamedTuple，Base1):x: 整数y:整数x = 测试 1(1, 2)x.foo() # 引发 AttributeError类 Base2(NamedTuple):def foo(self):打印(自我.__注释__)类 Test2(Base2):x: 整数y:整数x = Test2(1, 2) # TypeError: __new__() 需要 1 个位置参数，但给出了 3 个

有没有办法像这样使用 NamedTuple 类?

解决方案

问题在于 typing.NamedTuple 使用的元类；这个元类忽略所有基类，只生成一个带有添加注释信息的collections.namedtuple()类(复制直接定义在类上的任何附加属性).

您可以定义自己的元类(它必须是 typing.NamedTupleMeta 的子类)，在生成命名元组类之后添加额外的基类:

导入输入类 MultipleInheritanceNamedTupleMeta(typing.NamedTupleMeta):def __new__(mcls, typename, bases, ns):如果在基数中键入.NamedTuple:base = super().__new__(mcls, '_base_' + typename, bases, ns)bases = (base, *(b for b in bases if not isinstance(b, typing.NamedTuple)))return super(typing.NamedTupleMeta, mcls).__new__(mcls, typename, bases, ns)类 Base1(元类=MultipleInheritanceNamedTupleMeta):def foo(self):打印(自我.__注释__)类 Test1(NamedTuple，Base1):x: 整数y:整数

请注意，这不会让您继承字段！那是因为您必须为任何字段组合生成一个新的 namedtuple 类.以上产生了以下结构:

• Test1，继承自
  • _base_Test1 - 实际的 typing.NamedTuple 生成的 namedtuple
    • 元组
  • Base1

这按要求工作:

<预><代码>>>>x = 测试 1(1, 2)>>>x.foo(){'x':，'y':}

I'm using NamedTuples to hold data, and I want to add a method that can be inherited by multiple NamedTuple based classes. But when I try using multiple inheritance or subclassing NamedTuple based classes, it doesn't work. Specifically, I'm trying to automatically give all of my data classes a method that can look at the classes annotations and then call some serializing code based on that. Here are some examples of what I've tried:

from typing import NamedTuple


class Base1:
    def foo(self):
        print(self.__annotations__)


class Test1(NamedTuple, Base1):
    x: int
    y: int


x = Test1(1, 2)
x.foo() # raises AttributeError


class Base2(NamedTuple):
    def foo(self):
        print(self.__annotations__)


class Test2(Base2):
    x: int
    y: int


x = Test2(1, 2) # TypeError: __new__() takes 1 positional argument but 3 were given

is there a way for me to use the NamedTuple class like this?

解决方案

At issue is the metaclass used by typing.NamedTuple; this metaclass ignores all base classes and just generates a collections.namedtuple() class with added annotation information (copying across any additional attributes directly defined on the class).

You can define your own metaclass (which must be a subclass of typing.NamedTupleMeta), that adds your additional base classes after generating the named tuple class:

import typing

class MultipleInheritanceNamedTupleMeta(typing.NamedTupleMeta):
    def __new__(mcls, typename, bases, ns):
        if typing.NamedTuple in bases:
            base = super().__new__(mcls, '_base_' + typename, bases, ns)
            bases = (base, *(b for b in bases if not isinstance(b, typing.NamedTuple)))
        return super(typing.NamedTupleMeta, mcls).__new__(mcls, typename, bases, ns)

class Base1(metaclass=MultipleInheritanceNamedTupleMeta):
    def foo(self):
        print(self.__annotations__)

class Test1(NamedTuple, Base1):
    x: int
    y: int

Note that this won't let you inherit fields! That's because you must generate a new namedtuple class for any combination of fields. The above produces the following structure:

• Test1, inherits from
  • _base_Test1 - the actual typing.NamedTuple generated namedtuple
    • tuple
  • Base1

and this works as required:

>>> x = Test1(1, 2)
>>> x.foo()
{'x': <class 'int'>, 'y': <class 'int'>}

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