合并带嵌套元素的XML文件，无需外部库

Question

我正在尝试用Python把多个XML文件合并在一起，而且不想使用任何外部库。这些XML文件里面有嵌套的元素。

示例文件1：

<root>
  <element1>textA</element1>
  <elements>
    <nested1>text now</nested1>
  </elements>
</root>

示例文件2：

<root>
  <element2>textB</element2>
  <elements>
    <nested1>text after</nested1>
    <nested2>new text</nested2>
  </elements>
</root>

我想要的结果：

<root>
  <element1>textA</element1>    
  <element2>textB</element2>  
  <elements>
    <nested1>text after</nested1>
    <nested2>new text</nested2>
  </elements>  
</root>  

我尝试过的：

参考了这个回答。

from xml.etree import ElementTree as et
def combine_xml(files):
    first = None
    for filename in files:
        data = et.parse(filename).getroot()
        if first is None:
            first = data
        else:
            first.extend(data)
    if first is not None:
        return et.tostring(first)

我得到的结果：

<root>
  <element1>textA</element1>
  <elements>
    <nested1>text now</nested1>
  </elements>
  <element2>textB</element2>
  <elements>
    <nested1>text after</nested1>
    <nested2>new text</nested2>
  </elements>
</root>

我希望你能理解我的问题。我在寻找一个合适的解决方案，任何指导都会很棒。

为了更清楚地说明问题，使用我现在的解决方案时，嵌套的元素没有被合并。

Answer 1

在这里，我们扩展了@jadkik94的回答，创建了一个工具方法，这个方法不会改变它的参数，同时也会更新一些属性：

请注意，这段代码只在Python 2中有效，因为在Python 3中，Element类的copy()方法还不支持。

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
 

Answer 2

谢谢你，不过我的问题是要在合并的时候也考虑属性。下面是我修改后的代码：

    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)

Answer 3

你发的代码是在把所有的元素都合并在一起，不管之前有没有同样标签的元素。所以你需要一个一个地检查这些元素，手动地合并它们，按照你觉得合适的方式来做，因为这不是处理XML文件的标准方法。我没法比代码解释得更清楚了，下面是代码，里面有一些注释：

from xml.etree import ElementTree as et

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.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