How to print all the instances of a class in python?-CodePudding

I want to get all the instances created for a class. Is there any way to get the instances without importing any module ?

I tried this way to append self in a class attribute.

class A(object):
    instances = []

    def __init__(self, foo):
        self.foo = foo
        A.instances.append(self)
        
foo = A("hi")
bar = A("Hey")
star = A("Hero")

for instance in A.instances:
    print("Ins is ",instance)

Output

<__main__.A object at 0x148b8b6e0780>,
<__main__.A object at 0x148b8b6e0780>,
<__main__.A object at 0x148b8b6e0780>

I expect it to print foo,bar,star. Is there any way to get it in class without any module?

CodePudding user response：

Use this snippet:

for instance in A.instances:
    print("Ins is ", (instance.__dict__).get("foo"))

Output:

Ins is  hi
Ins is  Hey
Ins is  Hero

Or:

for instance in A.instances:
    print("Ins is ", instance.__dict__)

Output:

Ins is  {'foo': 'hi'}
Ins is  {'foo': 'Hey'}
Ins is  {'foo': 'Hero'}

To print an object, you can turn it into a dictionary. In this case, these values will be printable.

This method is usually used to convert objects to a dictionary and then to the JSON type, which is widely used to exchange information.

CodePudding user response：

you could do the following, if I got you right :

Proposal

tmp = globals().copy()
print(tmp)

for k,v in tmp.items():
    if isinstance(v, A):
        print(k)

You must copy the global variable dictionary, because otherwise i will be changed with the first instantiation in the for-loop:

Result:

foo
bar
star

CodePudding user response：

There is no way to define such behavior in a class, because the class assigns a value to a variable after instantiation. There is no way to get the name of the variable during class instantiation, because the variable does not exist yet