Someone

class Node:
    """
    General tree structure
    """
    def __init__(self,obj="",prof=1,call_me=None):
        self.obj = obj
        self.childs = []
        self.prof = prof
        self.call_me = None

    def __call__(self):
        if self.call_me:
            self.call_me()
        else:
            return "I m a simple node"

    def add_child(self,child):
        if not isinstance(child,Node):
            raise "child is not a Node"
        if child.obj in [my_childs.obj for my_childs in self.childs]:
            return
        self.childs.append(child)

    def is_atom(self):
        return bool(len(self.childs)==0)



def parcours_prof_gauche(node):
    results = [node()]
    if not node.is_atom():
        for child in node.childs:
            results.append(parcours_prof_gauche(child))
    return results