trees | Python Fiddle

class Tree(object):
    def __str__ (self):
        if self.right is None: 
            r= ""
        else: 
            r=str(self.right) 
        if self.left is None: 
            l= ""
        else: 
            l=str(self.left) 
        return "("+l+" "+self.id+" "+r+")"
        
    def __init__(self,id,right=None,left=None):
        self.right = right
        self.left = left
        self.id = id 
        
    def __add__(self,other):
        return Tree("",self,other)
            
        
    def __getitem__(self,id):
        if id=="L":
            return self.left
        elif id=="R":
            return self.right
        else:
        	raise ValueError('Invalid index:'+str(id))
            
    def __setitem__(self,id,value):
        if id=="L":
            self.left = value
        elif id=="R":
            self.right = value
        else:
        	raise ValueError('Invalid index:'+str(id))
            
try:
    root =Tree("R",Tree("2",Tree("3")),Tree("1",None,Tree("4",Tree("5"))))
    
    def rev(t) :
        if t is None:
            return None
        else:
            return Tree(t.id,rev(t.left),rev(t.right))
          
    print(root)
    print(rev(root))
    
    s = root+rev(root)
    s.id = "S"
    s["T"]="DUDU"
    s["R"]="BUBU"
    print(s)
except IOError as ioe:
    print("ERROR")
except ValueError as ve:
    print("Value error:"+str(ve))
except :
	print("ERROR")

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