Python Class Members Initialization

Question

I have just recently battled a bug in Python. It was one of those silly newbie bugs, but it got me thinking about the mechanisms of Python (I\'m a long time C++ programmer,

Answer 1

If this is your code:

class ClassA:
    dict1 = {}
a = ClassA()

Then you probably expected this to happen inside Python:

class ClassA:
    __defaults__['dict1'] = {}

a = instance(ClassA)
# a bit of pseudo-code here:
for name, value in ClassA.__defaults__:
    a. = value

As far as I can tell, that is what happens, except that a dict has its pointer copied, instead of the value, which is the default behaviour everywhere in Python. Look at this code:

a = {}
b = a
a['foo'] = 'bar'
print b