what is __slots__()?
see: https://wiki.python.org/moin/UsingSlots
it defines fix objects in a @dataclass
e.g dataclass without slots. we can define new_attribute in the instance
>>> @dataclass
... class Rect:
... height: int
... width: int
...
>>> r = Rect(1, 2)
>>> r
Rect(height=1, width=2)
>>> r.new_attribute = 5
>>> r.new_attribute
5
e.g dataclass with fixed attribute
>>> @dataclass
... class Circle:
... __slots__ = ("r", )
... r : int
...
>>> c = Circle(10)
>>> c
Circle(r=10)
>>> c.new_attribute = 5
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'Circle' object has no attribute 'new_attribute'
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