Question

I have an issue in Python I couldn’t believe to find out. See the following code:

class Container(object):
    array = []

    def __init__(self):
        print self.array

for i in range(0, 5):
    container = Container()
    container.array.append('Test')
print 'Last Container:', container.array

The output is:

[]
['Test']
['Test', 'Test']
['Test', 'Test', 'Test']
['Test', 'Test', 'Test', 'Test']
Last Container: ['Test', 'Test', 'Test', 'Test', 'Test']

I thought the Container class is initialized with the values at the top on instantiation. Why is this not the case?

Thank you!

Answer 1

Any attributes that you place directly inside of the class definition are class attributes, so Container.array is shared among all instances of Container.

If you want an instance attribute instead, set self.array = [] inside of __init__():

    def __init__(self):
        self.array = []
        print self.array