Merge xml files with nested elements without external libraries

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

Thank you, but my problem was to merge by considering the attributes also. here is the code after my patch:

    import sys    from xml.etree import ElementTree as et    class hashabledict(dict):        def __hash__(self):            return hash(tuple(sorted(self.items())))    class 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.ElementTree(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, hashabledict(el.attrib)): el for el in one}            for el in other:                if len(el) == 0:                    # Not nested                    try:                        # Update the text                        mapping[(el.tag, hashabledict(el.attrib))].text = el.text                    except KeyError:                        # An element with this name is not in the mapping                        mapping[(el.tag, hashabledict(el.attrib))] = 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, hashabledict(el.attrib))], el)                    except KeyError:                        # Not in the mapping                        mapping[(el.tag, hashabledict(el.attrib))] = el                        # Just add it                        one.append(el)if __name__ == '__main__':    r = XMLCombiner(sys.argv[1:-1]).combine()    print '-'*20    print et.tostring(r.getroot())    r.write(sys.argv[-1], encoding="iso-8859-1", xml_declaration=True)

Extending @jadkik94 's answer to create a utility method which doesn't change its argument and also updates the attributes:

Note the code works only in Py2 as copy() method of Element class is not yet supported in Py3.

def combine_xmltree_element(element_1, element_2):    """    Recursively combines the given two xmltree elements. Common properties will be overridden by values of those    properties in element_2.        :param element_1: A xml Element    :type element_1: L{Element}        :param element_2: A xml Element    :type element_2: L{Element}        :return: A xml element with properties combined.    """    if element_1 is None:        return element_2.copy()    if element_2 is None:        return element_1.copy()    if element_1.tag != element_2.tag:        raise TypeError(            "The two XMLtree elements of type {t1} and {t2} cannot be combined".format(                t1=element_1.tag,                t2=element_2.tag            )        )    combined_element = Element(tag=element_1.tag, attrib=element_1.attrib)    combined_element.attrib.update(element_2.attrib)    # Create a mapping from tag name to child element    element_1_child_mapping = {child.tag: child for child in element_1}    element_2_child_mapping = {child.tag: child for child in element_2}    for child in element_1:        if child.tag not in element_2_child_mapping:            combined_element.append(child.copy())    for child in element_2:        if child.tag not in element_1_child_mapping:            combined_element.append(child.copy())        else:            if len(child) == 0:  # Leaf element                combined_child = element_1_child_mapping[child.tag].copy()                combined_child.text = child.text                combined_child.attrib.update(child.attrib)            else:                # Recursively process the element, and update it in the same way                combined_child = combine_xmltree_element(element_1_child_mapping[child.tag], child)            combined_element.append(combined_child)    return combined_element