python __slots__ python__slots__ - Pythondataclass 在类级别创建一个固定的内存布局 Optimizing Python Classes with `__slots__`: A Deep Dive into Memory and Performance

Pythondataclass In the realm of Python programming, efficiently managing memory and optimizing performance are crucial for building robust and scalable applications2025114—To use __slots__ , we need todefine a __slots__ attribute on our classthat points to a tuple of strings that represent valid attributes names  One powerful, yet sometimes overlooked, feature that aids in this endeavor is `__slots__`__slots__ should not be a single string This special class attribute allows developers to explicitly declare a fixed set of attributes for instances of a class, offering significant advantages in terms of memory footprint and attribute access speedPython | Use of __slots__ - GeeksforGeeks Understanding python `__slots__` is key to unlocking these optimizationsShould You Use Slots? How Slots Affect Your Class, and

Understanding the `__slots__` Mechanism

At its core, `__slots__` is a special attribute you can define in a Python class to explicitly declare a fixed set of attributes for instances of that class20241123—__slots__ is a special attribute you can define in a Python classto explicitly declare a fixed set of attributes for instances of that class. This contrasts with the default behavior where each Python object typically has a `__dict__` attribute__slots__ should not be a single string This `__dict__` acts like a dictionary, allowing for dynamic attribute creation and modification at runtime10. __slots__ Magic — Python Tips 0.1 documentation While flexible, this dynamism comes at a cost20241217—__slots__ 的工作原理. 当我们使用__slots__ 时，Python 会：.在类级别创建一个固定的内存布局，类似C 语言中的结构体; 不再为实例创建__dict__ 和__ 

When you define `__slots__`, you are essentially instructing Python *not* to create an instance `__dict__` for objects of that class2018627—__slots__用于限制允许实例动态绑定的属性，__slots__中没有定义的属性实例无法动态绑定（这是__slots__的表面意义）. __slots__只能限制实例绑定属性，  Instead, Python will create a fixed set of instance variables for each object20211018—__slots__ 变量设置了类访问成员的活动范围，舍弃了原始Python类的灵活性，但是收益是类成员访问效率的提升。 slots 允许我们显式地声明数据成员（例如特征  This is often compared to how structures work in languages like C, where memory is allocated upfront for declared membersPython __slots__ 简介- 又见苍岚 The most common way to implement `__slots__` is by defining it as a tuple of strings, where each string represents a valid attribute name20211018—__slots__ 变量设置了类访问成员的活动范围，舍弃了原始Python类的灵活性，但是收益是类成员访问效率的提升。 slots 允许我们显式地声明数据成员（例如特征  For instance:

```python

class MyClass:

__slots__ = ('attribute1', 'attribute2')

def __init__(self, val1, val2):

self20191227—Usage of __slots__reduce the wastage of spaceand speed up the program by allocating space for a fixed amount of attributes.attribute1 = val1

self__slots__ should not be a single stringattribute2 = val2

```

In this example, any instance created from `MyClass` will only be able to hold `attribute1` and `attribute2`__slots__ for optimizing classes - Attempting to assign a new attribute, like `instance3. Data model — Python 3.14.2 documentationnew_attribute = 10`, will raise an `AttributeError`3. Data model — Python 3.14.2 documentation This mechanism is precisely what `slots__` uses to restrict certain instance bindings2025730—Are there any downsides tousing __slots__ in modern Python code? Just curious how often people reach for this in real-world projects.

The Benefits of Using `__slots__`

The primary motivations for using `__slots__` revolve around two key areas: memory usage and speedInvalid usages of classes with '__slots__' definitions

#### 1single-string-slots (PLC0205) | Ruff Reducing Memory Wastage and Optimizing Space

By eschewing the `__dict__`, instances of classes declared with `__slots__` consume significantly less memory2020826—You can avoid dynamic attributes creation by defining __slots__. Python will nowinstantiate a static amount of memoryto only contain the specified attributes. This is particularly beneficial when you are creating a large number of objects, such as in data-intensive applications or when working with collections of many small objectsWhy is this bad? In Python, the __slots__ attributeallows you to explicitly define the attributes (instance variables) that a class can have. By  The documentation highlights that `__slots__` reduces the wastage of space by allocating space for a fixed amount of attributes2022812—Python 3 a fait apparaître une déclaration d'attributs nommée slots. Pour mieux comprendre les __slots__ et leur puissance, expliquons d'abord  This means that Python will instantiate a static amount of memory to only contain the specified attributes, rather than relying on a dynamic dictionaryThe __slots__ attributemust be a non-string iterable. Learn More. Python Wiki Using slots. Non-Compliant Code Examples. class MyClass __slots__ = "attr 

#### 2When should I use __slots__ in a Python class, and what Speeding Up Attribute Access

Attribute access in Python typically involves a lookup within the `__dict__`Why is this bad? In Python, the __slots__ attributeallows you to explicitly define the attributes (instance variables) that a class can have. By  When `__slots__` is used, this lookup is bypassed, and attributes are accessed directly from their pre-allocated memory locationsWhen should I use __slots__ in a Python class, and what This can lead to a noticeable speed improvement, sometimes referred to as slots access being faster3. Data model — Python 3.14.2 documentation While the performance gains might be marginal for individual attribute accesses, they can compound significantly in performance-critical code that performs numerous attribute lookupsWhen should I use __slots__ in a Python class, and what

When to Use `__slots__`

While the benefits are clear, `__slots__` is not a silver bullet and should be employed judiciously__slots__ should not be a single string Here are some scenarios where using `__slots__` in modern Python code is highly recommended:

* Large Number of Objects: If your application creates many instances of a class, and memory is a concern, `__slots__` can drastically reduce the overall memory footprintsingle-string-slots (PLC0205) | Ruff

* Performance-Critical Code: In situations where attribute access speed is paramount, and you have a fixed set of attributes, `__slots__` can provide a performance boost2025123—Reports invalid usages of a class with __slots__ definitions. Example when accessing undefined attributes class Foo __slots__ = [ 

* Data Transfer Objects (DTOs) or Simple Data Structures: When a class primarily serves as a container for data with a predefined structure, `__slots__` is a natural fitWhy is this bad? In Python, the __slots__ attributeallows you to explicitly define the attributes (instance variables) that a class can have. By  This aligns with concepts like `Python dataclass` which often benefit from these optimizationsPython3 __slots__在类中的作用原创

* Implementing Enumerations with Attributes: As noted, they create a Python class who's name is the same as the enum typedef, and each member of the enumeration is defined as a member variable of the class, which can be efficiently managed with `__slots__`__slots__ for optimizing classes -

Understanding `__slots__` Limitations and Considerations

It's crucial to be aware of the trade-offs associated with `__slots__`:

#### 1What is __slots__ in Python? No `__dict__` and Dynamic Attributes

The most significant consequence of using `__slots__` is the absence of the `__dict__` attributeThey create a Python class who's name is the same as the enum typedef, and each member of the enumeration is defined as a member variable of the class. This means you cannot dynamically create new attributes on instances of classes that use `__slots__`3. Data model — Python 3.14.2 documentation If your use case requires dynamic attribute assignment, `__slots__` is not appropriate2025718—__slots__ are a double-edged sword. While they promise a leaner memory footprint and faster attribute access, they can silently backfire, creating performance  This also implies that features that rely on `__dict__`, such as certain forms of serialization or introspection, might not work as expectedApprendre les slots Python - Blog Ippon

#### 2When should I use __slots__ in a Python class, and what Inheritance with `__slots__`

Inheritance with `__slots__` can be complex__slots__ for optimizing classes - If a subclass defines its own `__slots__`, these slots are appended to the slots of the base classWhat is the purpose of __slots__ in Python? However, if a subclass *does not* define `__slots__`, it will automatically get a `__dict__` and `__weakref__` (if enabled), even if its base class uses `__slots__`10. __slots__ Magic — Python Tips 0.1 documentation This can lead to inconsistent memory usage__slots__. 3.3.3. Customizing class creation. 3.3.3.1. Metaclasses; 3.3.3.2 All data in aPythonprogram is represented by objects or by relations between  Therefore, it's generally recommended to either use `__slots__` consistently across an inheritance hierarchy or to be mindful of how it affects subclassesPython | Use of __slots__ - GeeksforGeeks

#### 3Python | Use of __slots__ - GeeksforGeeks `__slots__` Must Be an Iterable

A common pitfall is defining `__slots__` as a single string__slots__ should not be a single string The documentation clearly states that `__slots__` must be a non-string iterable2019327—通过实例了解python__slots__使用方法 它是在类定义中声明的一个元组，用于指定类实例能绑定的属性名称。在默认情况下，Python类的实例使用字典（`__dict  So, `__slots__ = "attribute"` is incorrect; it should be `__slots__ = ["attribute"]` or `__slots__ = ("attribute",)`single-string-slots (PLC0205) | Ruff Failure to adhere to this can lead to unexpected behavior or errorsWhat is the purpose of __slots__ in Python?

#### 4Slots allow you to use the return from a remote-execution functionas an argument value in states. Slot syntax looks close to the simple python function call. `__slots__` and `__weakref__`

By default, if a class defines `__slots__`, it does not automatically provide support for weak referencesIt involves the usage of __slots__ to tell Python not to use a dict, and only allocate space for a fixed set of attributes. If you need weak reference support, you must explicitly include `__weakref__` in your `__slots__` definition:

```python

class MyClassWithWeakRef:

__slots__ = ('attribute1', '__weakref__')

# Python `__slots__` 进阶指南：不止于节省内存，从原理到实践__slots__ Usage r/learnpythonPython `__slots__` 进阶指南：不止于节省内存，从原理到实践

```

#### 5python的__slots__ - Inkian Potential for "Broken `__slots__`"

As highlighted in some discussions, `__slots__` are a double-edged swordThe __slots__ attributemust be a non-string iterable. Learn More. Python Wiki Using slots. Non-Compliant Code Examples. class MyClass __slots__ = "attr  While they promise a leaner memory footprint and faster attribute access, they can silently backfire if not used correctly, potentially leading to performance issues or unexpected behaviorThe __slots__ attributemust be a non-string iterable. Learn More. Python Wiki Using slots. Non-Compliant Code Examples. class MyClass __slots__ = "attr  This emphasizes the need for careful implementation and testingInvalid usages of classes with '__slots__' definitions

`__slots__` in Context: Related Python Concepts

`__slots__` often appears in discussions alongside other Python features related to class definition and optimization:

* `Python metaclass`: Metaclasses control class creation itself__slots__ Usage r/learnpython While `__slots__` operates at the instance level by defining instance attributes, metaclasses can influence how classes are defined and behave__slots__ should not be a single string

* `Python @property`: The `@property` decorator allows you to define methods that can be accessed like attributesSlots allow you to use the return from a remote-execution functionas an argument value in states. Slot syntax looks close to the simple python function call. `__slots__` can be used in conjunction with `@property` to define the underlying storage for properties__slots__ Usage r/learnpython

* `Python attribute`: `__slots__` directly impacts how attributes are managed for class instances2025718—__slots__ are a double-edged sword. While they promise a leaner memory footprint and faster attribute access, they can silently backfire, creating performance 

* `Python __getattribute__`: This special method is called whenever an attribute lookup occurs2025730—Are there any downsides tousing __slots__ in modern Python code? Just curious how often people reach for this in real-world projects. If `__slots__` is used, the lookup mechanism is optimized and might bypass a direct call to `__getattribute__`20211018—__slots__ 变量设置了类访问成员的活动范围，舍弃了原始Python类的灵活性，但是收益是类成员访问效率的提升。 slots 允许我们显式地声明数据成员（例如特征 

* `Python __repr__` and `__str__`: These methods define the string representation of an object2020826—You can avoid dynamic attributes creation by defining __slots__. Python will nowinstantiate a static amount of memoryto only contain the specified attributes. If `__slots__` is used, you might need to manually implement `__repr__` and `__str__` to provide meaningful output, as standard methods might not behave as expected without a `__dict__`__slots__ Usage r/learnpython

Conclusion

The python `__slots__` mechanism is a powerful tool for Python developers aiming to optimize their code2025114—To use __slots__ , we need todefine a __slots__ attribute on our classthat points to a tuple of strings that represent valid attributes names  By allowing the explicit declaration of instance attributes, it can lead to significant reductions in memory consumption and improvements in attribute access speed20241123—__slots__ is a special attribute you can define in a Python classto explicitly declare a fixed set of attributes for instances of that class. Understanding how `slots` affect your class and adhering to best practices, such as ensuring `__slots__` must be a non-string iterable and being mindful of inheritance, are essential for harnessing its full potential__slots__ for optimizing classes - While `__slots__` are a double-edged sword, when applied judiciously in appropriate scenarios, they can be a vital component of building efficient and performant Python applicationsPython __slots__ 简介- 又见苍岚