def __init__(self, model1, model2):
self.model1 = model1<EOL>self.model2 = model2<EOL>self.width = {}<EOL>if model1.tree.tag == model2.tree.tag:<EOL><INDENT>self.tree = etree.Element(model1.tree.tag)<EOL>if id(self.model1) != id(self.model2):<EOL><INDENT>self.compare_nodes(model1.tree, model2.tree, self.tree)<EOL><DEDENT><DEDENT>else:<EOL><INDENT>raise ValueError("<STR_LIT>""<STR_LIT>".format(model1.tree.tag, model2.tree.tag))<EOL><DEDENT>
__init__ instantiates a Model instance.