Allocation de mémoire et référence

import sys

class MySemTree:
       
       def __init__(self,label,children=[]):
              self.label = label
              self.children=children
              
       def add_child(self,tree):
              self.children.append(tree)

       def dump(self,skip=3,indent=0):
              s =  self.label+'\n'
              for child in self.children:
                     print child.label
                     #s += child.dump(indent=indent+skip)
              return s

def add_branch(tree,lblist):    
       x = MySemTree(lblist[0])
       x.add_child(MySemTree('o'))
    
def yield_empty_tree():
       return MySemTree('-ROOT-')

root = yield_empty_tree()
add_branch(root,"XXX")
root.dump()

class bug:
  def __init__(self, data=[]):
    self.data = data

  def push(self, d):
    self.data.append(d)

  def show(self):
    print ' '.join(self.data)

a = bug()
a.push('Hello')
b = bug()
b.push('World!')
c = bug([])
c.push('Seul')

a.show()
b.show()
c.show()