[Python] Strange behavior of lists as class attributes [duplicate]

>>> class Abcd:
... a = ''
... menu = ['a', 'b', 'c']
...
>>> a = Abcd()
>>> b = Abcd()
>>> a.a = 'a'
>>> b.a = 'b'
>>> a.a
'a'
>>> b.a
'b'


It's all correct and each object has own 'a', but...

>>> a.menu.pop()
'c'
>>> a.menu
['a', 'b']
>>> b.menu
['a', 'b']


How could this happen? And how to use list as class attribute?

Continue reading...