Whether to use __slots__ depends on the scenario. 1. Using __slots__ when creating a large number of objects can significantly reduce memory usage; 2. If you want to prevent __slots__ from being used to improve code security when adding properties dynamically; 3. Pay attention to the influence of the parent class, the inability to use __dict__ and the restrictions that may conflict with third-party libraries; 4. If you do not need to use small scripts or dynamic properties, you need them.
Using __slots__ in Python classes can bring performance and memory optimization, but not all cases require it. Its main function is to limit the properties that an instance of a class can have and reduce memory usage. Whether to use __slots__ depends on your usage scenario.
Here are some common applicable situations and suggestions:
1.When you create a large number of objects
If your application creates thousands of instances of a certain class, such as processing data models, minion units in the game, log entries, etc., then using __slots__ can significantly reduce memory overhead.
Python maintains a __dict__ property for each instance by default, and this dictionary structure itself takes up a lot of space. After using __slots__ , these properties will be stored more compactly, saving memory.
example:
class Point:
__slots__ = ('x', 'y')
def __init__(self, x, y):
self.x = x
self.y = y Compared with the version without adding __slots__ , this writing can significantly reduce memory consumption when creating 100,000 or even millions of points.
2. When you want to prevent dynamic addition of attributes
Sometimes you don't want the instance of the class to be added at will, such as for the maintainability of the code or to avoid bugs caused by typos.
When __slots__ is not added, the user may operate incorrectly:
p = Point(1, 2) pz = 3 # No error is reported, but the logic may be errored
If __slots__ is defined and 'z' is not included, the above line of code will directly throw an exception and find the problem in advance.
Situations suitable for this need include:
- Data model classes (such as entities in ORM)
- Data containers for configuration classes or fixed structures
- Public API interface parameter object
3. Pay attention to places that cannot be used casually
Although __slots__ has many benefits, there are some limitations to pay attention to:
- If the parent class uses
__slots__, the subclass must also be handled carefully, otherwise the expected results may not be achieved. - Classes that use
__slots__can no longer have dynamic properties, and they cannot use__dict__and__weakref__(unless explicitly declared). - Some frameworks (such as some serialization libraries or debugging tools) rely on
__dict__and may be handled unfriendly to__slots__class.
So before deciding to use it, first confirm whether it will affect the third-party library or debugging method you are using.
4. When can I not use it?
If you just write a small script, tool class, or just create a small number of objects, there is actually no need to use __slots__ . At this time, a clear code structure is more important than this performance improvement.
Also, if you do need to add properties dynamically, don't think about it at all.
Basically that's it. To sum up, use __slots__ in scenarios where a large number of objects or attributes need to be restricted, and keep it simple at other times.
The above is the detailed content of When to use __slots__ in a Python class?. For more information, please follow other related articles on the PHP Chinese website!
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