View source for The Use of slots in Python Classes

=Summary=

In Python, the __slots__ attribute is a mechanism that allows you to explicitly declare a set of attributes for a class. This declaration restricts the creation of new attributes in instances of that class, which can help in reducing memory overhead and improving attribute access speed.

Here's a basic overview of how __slots__ works:

# Memory Optimization: When you create an instance of a class, Python creates a dictionary to store the instance's attributes and their values. This dictionary incurs some memory overhead. If a class has a fixed set of attributes, using __slots__ can be more memory-efficient because it avoids the need for a dynamic dictionary.

# Attribute Restriction: By using __slots__, you limit the attributes that instances of a class can have. Any attempt to create a new attribute that is not listed in __slots__ will result in an AttributeError. This can be useful in preventing accidental creation of new attributes and enforcing a strict attribute structure.

Here's an example:

<pre>
class SomeClass:
    __slots__ = ('attribute1', 'attribute2')

    def __init__(self, value1, value2):
        self.attribute1 = value1
        self.attribute2 = value2

# Creating an instance

obj = SomeClass('value1', 'value2')

# Accessing attributes

print(obj.attribute1)  # Output: value1
print(obj.attribute2)  # Output: value2

# Attempting to create a new attribute
# This will raise an AttributeError

obj.new_attribute = 'new_value'
</pre>

Keep in mind the following considerations:

The __slots__ attribute is a tuple of attribute names, and it should be defined at the class level.

Instances of classes with __slots__ use a different mechanism to store attributes, which can result in some restrictions, such as the inability to use certain features like __dict__ and weak references.

* Using __slots__ is primarily beneficial when you have a large number of instances of a class and want to optimize memory usage.
* While __slots__ can be useful in certain scenarios, it's essential to carefully consider whether the benefits outweigh the trade-offs, especially in terms of flexibility and maintainability.