What the code you posted is doing is combining all the elements regardless of whether or not an element with the same tag already exists. So you need to iterate over the elements and manually check and combine them the way you see fit, because it is not a standard way of handling XML files. I can't explain it better than code, so here it is, more or less commented:
from xml.etree import ElementTree as etclass XMLCombiner(object): def __init__(self, filenames): assert len(filenames) > 0, 'No filenames!' # save all the roots, in order, to be processed later self.roots = [et.parse(f).getroot() for f in filenames] def combine(self): for r in self.roots[1:]: # combine each element with the first one, and update that self.combine_element(self.roots[0], r) # return the string representation return et.tostring(self.roots[0]) def combine_element(self, one, other):""" This function recursively updates either the text or the children of an element if another element is found in `one`, or adds it from `other` if not found.""" # Create a mapping from tag name to element, as that's what we are fltering with mapping = {el.tag: el for el in one} for el in other: if len(el) == 0: # Not nested try: # Update the text mapping[el.tag].text = el.text except KeyError: # An element with this name is not in the mapping mapping[el.tag] = el # Add it one.append(el) else: try: # Recursively process the element, and update it in the same way self.combine_element(mapping[el.tag], el) except KeyError: # Not in the mapping mapping[el.tag] = el # Just add it one.append(el)if __name__ == '__main__': r = XMLCombiner(('sample1.xml', 'sample2.xml')).combine() print '-'*20 print r