How to Print All Instances of a Python Class?

Printing Specific Instances of a Class in Python

When defining a Python class, it can be useful to create a function that outputs every instance of the class in a custom format. There are multiple approaches to achieving this goal.

Utilizing the Garbage Collector

One option involves utilizing the garbage collector:

<code class="python">import gc

for obj in gc.get_objects():
    if isinstance(obj, some_class):
        dome_something(obj)</code>

However, this method can be sluggish when dealing with numerous objects and is only applicable to types within your control.

Employing a Mixin and WeakRefs

Alternatively, you can implement a mixin and weak references as follows:

<code class="python">from collections import defaultdict
import weakref

class KeepRefs(object):
    __refs__ = defaultdict(list)

    def __init__(self):
        self.__refs__[self.__class__].append(weakref.ref(self))

    @classmethod
    def get_instances(cls):
        for inst_ref in cls.__refs__[cls]:
            inst = inst_ref()
            if inst is not None:
                yield inst</code>

This approach stores references as weak references within a list. To ensure efficiency, consider cleaning up the weakrefs after iteration, especially when dealing with frequent instance creation and deletion. Also, note that this technique is limited to classes under your control.

The specific format for printing instances can be implemented via custom for-loops. Implementing this printing format is left as an exercise for further understanding.

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