`weakref`

The Python weakref module provides tools for creating weak references to objects for efficient memory management. With weak references, you can cache objects, track their lifecycle, and automatically clean up resources—all without worrying about memory leaks.

Here’s a quick example:

Python
      
        
      
    
>>> import weakref

>>> class DemoClass:
...     pass
...

>>> obj = DemoClass()
>>> weak_obj = weakref.ref(obj)
>>> weak_obj()
<__main__.DemoClass object at 0x...>
>>> del obj
>>> weak_obj() is None
True

Key Features

Creates weak references to objects
Allows for callbacks when objects are about to be finalized
Supports weak dictionaries and sets
Provides tools for tracking object lifecycle
Integrates with custom finalization and resource cleanup
Offers advanced memory management for complex applications
Helps prevent memory leaks in caches and other data structures

Frequently Used Classes and Functions

Object	Type	Description
`weakref.ref()`	Class	Creates a weak reference to an object
`weakref.WeakValueDictionary`	Class	Implements a dictionary that stores only weak references to values
`weakref.WeakKeyDictionary`	Class	Implements a dictionary that stores only weak references to keys
`weakref.finalize()`	Function	Registers a callback to be invoked when an object is garbage collected
`weakref.getweakrefcount()`	Function	Returns the number of weak references to an object
`weakref.getweakrefs()`	Function	Returns a list of weak reference objects for an object

Examples

Using WeakValueDictionary to manage cache:

Python
      
>>> import weakref

>>> cache = weakref.WeakValueDictionary()
>>> cache["item"] = DemoClass()
>>> "item" in cache
True

Common Use Cases

Implementing caches that do not prevent their items from being garbage collected
Creating mappings where keys or values are allowed to be garbage collected
Using callbacks for cleanup operations when objects are about to be destroyed
Tracking objects for resource management or debugging
Automatically cleaning up related resources or files
Building data structures that require dynamic object management

Real-World Example

Suppose you want to cache objects but allow them to be garbage collected when they’re no longer in use elsewhere. You can use WeakValueDictionary to achieve this:

Python
      
        
      
    
>>> import weakref

>>> class Data:
...     def __init__(self, name):
...         self.name = name
...
...     def __repr__(self):
...         return f"Data({self.name!r})"
...

>>> cache = weakref.WeakValueDictionary()
>>> data = Data("item")
>>> cache["data"] = data
>>> del data
>>> "data" in cache
False

In this example, you add data to the cache, but it’s garbage collected when there are no strong references to it, demonstrating how weakref helps manage memory efficiently.

Tutorial

Memory Management in Python

Get ready for a deep dive into the internals of Python to understand how it handles memory management. By the end of this article, you’ll know more about low-level computing, understand how Python abstracts lower-level operations, and find out about Python’s internal memory management algorithms.

intermediate python

For additional information on related topics, take a look at the following resources: