Are the children of Python data classes always data classes themselves?-CodePudding

Suppose I create a parent class and a child class in Python like so:

@dataclass
class MyParent:
    an_attribute: str = "Hello!"
    another_attribute: str = "Dave!"

@dataclass
class MyChild(MyParent):
    another_attribute: str = "Steve!"

Then, clearly, both MyParent and MyChild will be data classes.

But, what happens if I use the following syntax to create MyChild instead?

class MyChild(MyParent):
    another_attribute: str = "Steve!"

Testing on my own machine suggests that, even with the latter syntax, MyChild will also be a data class. But are the children of data classes always data classes themselves? Are there any pitfalls to the latter approach? Is the @dataclass decorator essentially redundant in the definition of the child?

CodePudding user response：

Adding the decorator again is required. Without it, the fields of the child class are not created properly.

>>> @dataclass
... class MyParent:
...     an_attribute: str = "Hello!"
...     another_attribute: str = "Dave!"
... 
... class MyChild(MyParent):
...     another_attribute: str = "Steve!"
... 
>>> MyChild().another_attribute  # returns the incorrect default
'Dave!'

CodePudding user response：

The dataclass magic is not triggered for the non-dataclass version of My_Child, although it will inherit the special dataclass attributes (__dataclass_fields__ etc) from My_Parent, but only for the parent's attributes

Try this:

class MyChild(MyParent):
    another_attribute: str = "Steve!"
    yet_another_attribute : str = "Mickey!"

You will see that yet_another_attribute is a class member, not an instance one