Python elementtree and mutability -

what doing wrong python (2.7) here?

i using element trees store xml data. class constructor takes class instance element tree attribute (sw class insance, sw.instance element tree) parameter, adds element , stores in class variable self.software. class constructor:

import xml.etree.elementtree elt class myclass(object):     def __init__(self, bd, sw, name):         itmp = sw.instance         print "before %s" % elt.tostring(itmp)         y = elt.subelement(itmp, "name")         y.text = name         self.software = itmp         print "after %s" % elt.tostring(sw.instance) 

the problem is, in addition of storing modified sw self.software, changes sw.instance. when use create 2 classes

foo = myclass(x, mysoftwareclass, "foo") bar = myclass(y, mysoftwareclass, "bar") 

the foo instance fine bar instance contains 2 "name" elements. first call myclass appears modify mysoftwareclass instance. have confirmed before , after print statements.

i sort of thought mysoftwareclass immutable when called this. can of course use workaround , create 2 identical software class instances, pass 1 foo , 1 bar, curious happens here.

found it. copy.deepcopy. how stupid of me.