Python - Reset value for all instances of the same class

in a Ren'Py game I'm coding, I'm trying to optimize my code, and I'm stuck at finding a way to reset a the same value for all instances of a same class.

Here's my code :

init python:
    class Girl():
        def __init__(self,name,age):
            self.name = name
            self.age = age
            self.place = "Nowhere"
            self.appear = False

   Bree = Girl("Bree",26)
   Sasha = Girl("Sasha",27)

label reset_appear():
    Bree.appear = False
    Sasha.appear = False

For now I only have a few instances of that class, but I'm planning on adding something like 50 more, and I wanted to fix that before continuing.

I thought of doing something like this (still while in class):

def reset_appear(self):
    self.appear = False

But you'll still need to call it for each instance. I also thought of the same function outside of the class, but I don't know how to code it.

I'm not familiar with Ren'Py, so my examples are in normal Python.

You need somewhere a collection of all instances of the Girl class. This could be either with a plain list:

class Girl():
    def __init__(self,name,age):
        self.name = name
        self.age = age
        self.place = "Nowhere"
        self.appear = False

Bree = Girl("Bree", 26)
Sasha = Girl("Sasha", 27)
girls = [Bree, Sasha]

for girl in girls:
    girl.appear = False

Or you could have the class handle it:

class Girl():
    instances = []

    def __init__(self,name,age):
        Girl.instances.append(self)
        self.name = name
        self.age = age
        self.place = "Nowhere"
        self.appear = False

for girl in Girl.instances:
    girl.appear = False