Python 3.7：dataclass不会为`eq = False`引发`TypeError`

我在Python 3.7中尝试新的数据类

可以传递dataclass装饰器参数来控制添加到类中的dunder函数.

出于某种原因,装饰器似乎没有为eq = False参数引发TypeError.

根据文档：

eq: If true (the default), an __eq__ method will be generated. 
This method compares the class as if it were a tuple of its fields, in order. 
Both instances in the comparison must be of the identical type

如果我理解正确,如果我传递eq = False,则不会添加__eq__函数,并且在比较同一类的两个实例时应该抛出TypeError.相反,eq参数似乎没有任何效果.

@dataclass(eq = False)
class Number:
    val: int

a = Number(1)
b = Number(2)
c = Number(1)

a == b
False

a == c
False

以上不会引发TypeError并始终计算为False.

@dataclass()
class Number:
    val: int

a = Number(1)
b = Number(2)
c = Number(1)

a
Number(val = 1)

a == b
False

a == c
True

其他参数(例如：order,repr)似乎表现得如预期的那样

@dataclass(order = False, repr = False)
class Number:
    val:int

a = Number(1)
b = Number(2)
c = Number(1)

a
<__main__.Number object at 0x7fe1036c8b38>

a < b
Traceback (most recent call last):                                                                                                          
  File "<stdin>", line 1, in <module>                                                                                                       
TypeError: '<' not supported between instances of 'Number' and 'Number' 

我的理解是否存在一些差距？

我正在使用docker image python / rc-stretch

解决方法:

在python3.7中,给出了以下数据类定义

@dataclass(eq=False)
class Number:
    val: int

Number(1)== Number(1)的预期结果为False.这是正确的,因为设置eq = True只会覆盖the default python-object equality function,在这种情况下,它仅检查相同的引用(与is相同).

dataclass specification在这里有点缺乏.它解释了eq参数

eq: If true (the default), an __eq__ method will be generated. This method compares the class as if it were a tuple of its fields, in order. […]

但是为了理解你遇到的问题,你还需要知道基本的python对象已经提供了一个__eq__函数：

>>> class A: pass
...
>>> dir(A())
['__class__', '__delattr__', ... '__eq__', ...]  # has __eq__ already

标签：python,python-3-7,python-dataclasses
来源： https://codeday.me/bug/20190910/1801790.html