python __slots__ using __slots__ in modern Python code - Python描述 符 slots__ are a double-edged sword Optimizing Python Classes with `__slots__`: A Deep Dive into Memory and Performance

Python@property In the realm of Python programming, efficiently managing memory and optimizing performance are crucial for building robust and scalable applications2019327—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  One powerful, yet sometimes overlooked, feature that aids in this endeavor is `__slots__`The __slots__ attributemust be a non-string iterable. Learn More. Python Wiki Using slots. Non-Compliant Code Examples. class MyClass __slots__ = "attr  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 speed10. __slots__ Magic — Python Tips 0.1 documentation Understanding python `__slots__` is key to unlocking these optimizationsPython `__slots__` 进阶指南：不止于节省内存，从原理到实践

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 classIt involves the usage of __slots__ to tell Python not to use a dict, and only allocate space for a fixed set of attributes. This contrasts with the default behavior where each Python object typically has a `__dict__` attribute2023812—Slots are a mechanism that allow you to declare class attributesand restrict the creation of other attributes. This `__dict__` acts like a dictionary, allowing for dynamic attribute creation and modification at runtimepython的__slots__ - Inkian While flexible, this dynamism comes at a cost__slots__ should not be a single string

When you define `__slots__`, you are essentially instructing Python *not* to create an instance `__dict__` for objects of that classPython `__slots__` 进阶指南：不止于节省内存，从原理到实践 Instead, Python will create a fixed set of instance variables for each object2025123—Reports invalid usages of a class with __slots__ definitions. Example when accessing undefined attributes class Foo __slots__ = [  This is often compared to how structures work in languages like C, where memory is allocated upfront for declared membersThe __slots__ attributemust be a non-string iterable. Learn More. Python Wiki Using slots. Non-Compliant Code Examples. class MyClass __slots__ = "attr  The most common way to implement `__slots__` is by defining it as a tuple of strings, where each string represents a valid attribute name2023812—Slots are a mechanism that allow you to declare class attributesand restrict the creation of other attributes. For instance:

```python

class MyClass:

__slots__ = ('attribute1', 'attribute2')

def __init__(self, val1, val2):

self2018627—__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， attribute1 = val1

selfSlots - Salt docs - Saltproject.ioattribute2 = val2

```

In this example, any instance created from `MyClass` will only be able to hold `attribute1` and `attribute2`Python `__slots__` 进阶指南：不止于节省内存，从原理到实践 Attempting to assign a new attribute, like `instanceWhen should I use __slots__ in a Python class, and what new_attribute = 10`, will raise an `AttributeError`python的__slots__ - Inkian 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 speedThey 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.

#### 12025730—Are there any downsides tousing __slots__ in modern Python code? Just curious how often people reach for this in real-world projects. Reducing Memory Wastage and Optimizing Space

By eschewing the `__dict__`, instances of classes declared with `__slots__` consume significantly less memoryThey 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 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 objects2018627—__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，  The documentation highlights that `__slots__` reduces the wastage of space by allocating space for a fixed amount of attributesPython | Use of __slots__ - GeeksforGeeks This means that Python will instantiate a static amount of memory to only contain the specified attributes, rather than relying on a dynamic dictionary3. Data model — Python 3.14.2 documentation

#### 2Python | Use of __slots__ - GeeksforGeeks Speeding Up Attribute Access

Attribute access in Python typically involves a lookup within the `__dict__`Python `__slots__` 进阶指南：不止于节省内存，从原理到实践 When `__slots__` is used, this lookup is bypassed, and attributes are accessed directly from their pre-allocated memory locations2018627—__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，  This can lead to a noticeable speed improvement, sometimes referred to as slots access being fasterSlots 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. While the performance gains might be marginal for individual attribute accesses, they can compound significantly in performance-critical code that performs numerous attribute lookupsPython __slots__ 简介- 又见苍岚

When to Use `__slots__`

While the benefits are clear, `__slots__` is not a silver bullet and should be employed judiciously20241123—__slots__ is a special attribute you can define in a Python classto explicitly declare a fixed set of attributes for instances of that class. 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 footprintPython __slots__ 简介- 又见苍岚

* Performance-Critical Code: In situations where attribute access speed is paramount, and you have a fixed set of attributes, `__slots__` can provide a performance boostsingle-string-slots (PLC0205) | Ruff

* 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 optimizationsBroken __slots__ are a silent performance killer—Let's fix

* 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__`2025718—__slots__ are a double-edged sword. While they promise a leaner memory footprint and faster attribute access, they can silently backfire, creating performance 

Understanding `__slots__` Limitations and Considerations

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

#### 1When should I use __slots__ in a Python class, and what No `__dict__` and Dynamic Attributes

The most significant consequence of using `__slots__` is the absence of the `__dict__` attributeSlots - Salt docs - Saltproject.io This means you cannot dynamically create new attributes on instances of classes that use `__slots__`2020826—You can avoid dynamic attributes creation by defining __slots__. Python will nowinstantiate a static amount of memoryto only contain the specified attributes. If your use case requires dynamic attribute assignment, `__slots__` is not appropriate__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  This also implies that features that rely on `__dict__`, such as certain forms of serialization or introspection, might not work as expected__slots__ should not be a single string

#### 22022812—Python 3 a fait apparaître une déclaration d'attributs nommée slots. Pour mieux comprendre les __slots__ et leur puissance, expliquons d'abord  Inheritance with `__slots__`

Inheritance with `__slots__` can be complexWhy is this bad? In Python, the __slots__ attributeallows you to explicitly define the attributes (instance variables) that a class can have. By  If a subclass defines its own `__slots__`, these slots are appended to the slots of the base class2020826—You can avoid dynamic attributes creation by defining __slots__. Python will nowinstantiate a static amount of memoryto only contain the specified attributes. 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__`__slots__ Usage r/learnpython This can lead to inconsistent memory usageWhat is the purpose of __slots__ in Python? Therefore, it's generally recommended to either use `__slots__` consistently across an inheritance hierarchy or to be mindful of how it affects subclasses2025123—Reports invalid usages of a class with __slots__ definitions. Example when accessing undefined attributes class Foo __slots__ = [ 

#### 3__slots__ should not be a single string `__slots__` Must Be an Iterable

A common pitfall is defining `__slots__` as a single string__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  The documentation clearly states that `__slots__` must be a non-string iterable20241123—__slots__ is a special attribute you can define in a Python classto explicitly declare a fixed set of attributes for instances of that class. So, `__slots__ = "attribute"` is incorrect; it should be `__slots__ = ["attribute"]` or `__slots__ = ("attribute",)`Should You Use Slots? How Slots Affect Your Class, and Failure to adhere to this can lead to unexpected behavior or errorsSlots - Salt docs - Saltproject.io

#### 420191227—Usage of __slots__reduce the wastage of spaceand speed up the program by allocating space for a fixed amount of attributes. `__slots__` and `__weakref__`

By default, if a class defines `__slots__`, it does not automatically provide support for weak references__slots__ for optimizing classes - If you need weak reference support, you must explicitly include `__weakref__` in your `__slots__` definition:

```python

class MyClassWithWeakRef:

__slots__ = ('attribute1', '__weakref__')

# Slots - Salt docs - Saltproject.ioIt involves the usage of __slots__ to tell Python not to use a dict, and only allocate space for a fixed set of attributes.What is __slots__ in Python?

```

#### 52018627—__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，  Potential for "Broken `__slots__`"

As highlighted in some discussions, `__slots__` are a double-edged swordpython的__slots__ - Inkian 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 testing10. __slots__ Magic — Python Tips 0.1 documentation

`__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 itself2025123—Reports invalid usages of a class with __slots__ definitions. Example when accessing undefined attributes class Foo __slots__ = [  While `__slots__` operates at the instance level by defining instance attributes, metaclasses can influence how classes are defined and behave20211018—__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 @property`: The `@property` decorator allows you to define methods that can be accessed like attributesThe __slots__ attributemust be a non-string iterable. Learn More. Python Wiki Using slots. Non-Compliant Code Examples. class MyClass __slots__ = "attr  `__slots__` can be used in conjunction with `@property` to define the underlying storage for propertiesSlots 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.

* `Python attribute`: `__slots__` directly impacts how attributes are managed for class instances2022812—Python 3 a fait apparaître une déclaration d'attributs nommée slots. Pour mieux comprendre les __slots__ et leur puissance, expliquons d'abord 

* `Python __getattribute__`: This special method is called whenever an attribute lookup occursWhat is the purpose of __slots__ in Python? If `__slots__` is used, the lookup mechanism is optimized and might bypass a direct call to `__getattribute__`Apprendre les slots Python - Blog Ippon

* `Python __repr__` and `__str__`: These methods define the string representation of an objectSlots - Salt docs - Saltproject.io 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__`Should You Use Slots? How Slots Affect Your Class, and

Conclusion

The python `__slots__` mechanism is a powerful tool for Python developers aiming to optimize their codepython的__slots__ - Inkian By allowing the explicit declaration of instance attributes, it can lead to significant reductions in memory consumption and improvements in attribute access speed2025114—To use __slots__ , we need todefine a __slots__ attribute on our classthat points to a tuple of strings that represent valid attributes names  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 potentialThe __slots__ attributemust be a non-string iterable. Learn More. Python Wiki Using slots. Non-Compliant Code Examples. class MyClass __slots__ = "attr  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 applications2023812—Slots are a mechanism that allow you to declare class attributesand restrict the creation of other attributes.