python: copy by reference, copy by value, shit it depends on what you copy!

class MyClass:                                                                  
    def __init__(self):                                                         
        self.__data = []                                                        
        self.doSomething()                                                      
    def doSomething(self):                                                      
        #[self.__buckets.append([1,2,i] ) for i in range (0,4)]                 
        [self.__data.append(i ) for i in range (0,4)]                           
    def getData(self):                                                          
        return self.__data                                                      
    def modBucket(self):                                                        
        h = self.__data[2]                                                      
        h = 5                                                                   
    def modBucket2(self):                                                       
        h = self.__data                                                         
        h[2] = 5                                                                

c = MyClass()                                                                   
print "init:", c.getData()                                                      
c.modBucket()                                                                   
print "mod1:", c.getData()                                                      
c.modBucket2()                                                                  
print "mod2:", c.getData()                                                      
print "-------------------------"                                                                               

The output of running this code is:

init: [0, 1, 2, 3]
mod1: [0, 1, 2, 3]
mod2: [0, 1, 5, 3]
------------------------ 

Notice the problem, if you ask for the whole object, you get if by reference, if you ask for a part of it, you get a copy!!!!
Haven’t yet found the logic for this, any directions welcome.