Is there a way to run a method for all instances of a class in python?

Question

Example code:

>>> class MyClass(object):
        def __init__(self, x, y):
            self.x = x
            self.y = y
        def power(self):
            print(self.x**self.y)
        def divide(self):
            print(self.x/self.y)

>>> foo = MyClass(2, 3)
>>> bar = MyClass(4, 7)
>>> 
>>> foo.power()
8
>>> bar.divide()
0.5714285714285714

Whenever I used classes in Python previously, I just ran the method for each instance separately (see above). I was just wondering If there was a way to run the same method for all the instances of that class at once, because it could get a bit annoying, if you have 20 or so instances. I'm thinking of something like this:

>>> allinstances.power()
8
16384

Is there a way of doing this?

Answer 1

class MyClass(object):

    instancelist = []

    def __init__(self, x, y):
        self.x = x
        self.y = y
        MyClass.instancelist.append(self)

    def power(self):
        print(self.x ** self.y)

    def divide(self):
        print(self.x / self.y)


foo = MyClass(2, 3)
bar = MyClass(4, 7)

[instance.power() for instance in MyClass.instancelist]

will output:

8
16384

This way you do not need any global variables or placeholders that are stored outside of the class definition.

Answer 2

Not usually. You could make your class be capable of that, however:

GLOBAL_MYCLASS_LIST = []

class MyClass(object):

    def __init__(self, x, y):
        GLOBAL_MYCLASS_LIST.append(self)
        self.x = x
        self.y = y

    def power(self):
        print(self.x**self.y)

    def divide(self):
        print(self.x/self.y)

a = MyClass(2, 3)
b = MyClass(4, 7)
all_powers = [i.power() for i in GLOBAL_MYCLASS_LIST]

Of course, you could also do that without baking it into the class, which is probably cleaner for most cases where you might have different sets of MyClasses:

myclass_list = []

class MyClass(object):

    def __init__(self, x, y):
        self.x = x
        self.y = y

    def power(self):
        print(self.x**self.y)

    def divide(self):
        print(self.x/self.y)

myclass_list.append(MyClass(2, 3))
myclass_list.append(MyClass(4, 7))
all_powers = [i.power() for i in myclass_list]