def __init__(self, anchor=None):
        """Create a new item to be inserted before item anchor.
           if anchor is None: create a single item circular double linked list
        """
        if anchor:
            self.insert(anchor)
        else:
            self.prec = self
            self.succ = self
def __init__ ( self , anchor = None ) : if anchor : self . insert ( anchor ) else : self . prec = self self . succ = self
Create a new item to be inserted before item anchor.
           if anchor is None: create a single item circular double linked list