回溯的变量变化

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Publish Date:   2023-02-11
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递归回溯涉及到的变量变化

def parse_xml_to_dict(self, xml):

        if len(xml) == 0:  # 遍历到底层，直接返回tag对应的信息
            return {xml.tag: xml.text}

        result = {}
        print("bbb")
        for child in xml:
            print("aaa")
            child_result = parse_xml_to_dict(child)  # 递归遍历标签信息
            print(result)
            
            # if child.tag != 'object':
            result[child.tag] = child_result[child.tag]
            print(result)
            # else:
            #     if child.tag not in result:  # 因为object可能有多个，所以需要放入列表里
            #         result[child.tag] = []
            #     result[child.tag].append(child_result[child.tag])
        return {xml.tag: result}

输入数据：


<annotation>
    <folder>VOC2007</folder>
    <filename>000001.jpg</filename>
    <source>
        <database>The VOC2007 Database</database>
        <annotation>PASCAL VOC2007</annotation>
        <image>flickr</image>
        <flickrid>341012865</flickrid>
    </source>
    <owner>
        <flickrid>Fried Camels</flickrid>
        <name>Jinky the Fruit Bat</name>
    </owner>
    <size>
        <width>353</width>
        <height>500</height>
        <depth>3</depth>
    </size>
    <segmented>0</segmented>
    <object>
        <name>dog</name>
        <pose>Left</pose>
        <truncated>1</truncated>
        <difficult>0</difficult>
        <bndbox>
            <xmin>48</xmin>
            <ymin>240</ymin>
            <xmax>195</xmax>
            <ymax>371</ymax>
        </bndbox>
    </object>
    <object>
        <name>person</name>
        <pose>Left</pose>
        <truncated>1</truncated>
        <difficult>0</difficult>
        <bndbox>
            <xmin>8</xmin>
            <ymin>12</ymin>
            <xmax>352</xmax>
            <ymax>498</ymax>
        </bndbox>
    </object>
</annotation>

输出如下：

bbb
aaa
{}
{'folder': 'VOC2007'}
aaa
{'folder': 'VOC2007'}
{'folder': 'VOC2007', 'filename': '000001.jpg'}
aaa
bbb
aaa
{}
{'database': 'The VOC2007 Database'}
aaa
{'database': 'The VOC2007 Database'}
{'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007'}
aaa
{'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007'}
{'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr'}
aaa
{'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr'}
{'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}
{'folder': 'VOC2007', 'filename': '000001.jpg'}
{'folder': 'VOC2007', 'filename': '000001.jpg', 'source': {'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}}
aaa
bbb
aaa
{}
{'flickrid': 'Fried Camels'}
aaa
{'flickrid': 'Fried Camels'}
{'flickrid': 'Fried Camels', 'name': 'Jinky the Fruit Bat'}
{'folder': 'VOC2007', 'filename': '000001.jpg', 'source': {'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}}
{'folder': 'VOC2007', 'filename': '000001.jpg', 'source': {'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}, 'owner': {'flickrid': 'Fried Camels', 'name': 'Jinky the Fruit Bat'}}
aaa
bbb
aaa
{}
{'width': '353'}
aaa
{'width': '353'}
{'width': '353', 'height': '500'}
aaa
{'width': '353', 'height': '500'}
{'width': '353', 'height': '500', 'depth': '3'}
{'folder': 'VOC2007', 'filename': '000001.jpg', 'source': {'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}, 'owner': {'flickrid': 'Fried Camels', 'name': 'Jinky the Fruit Bat'}}
{'folder': 'VOC2007', 'filename': '000001.jpg', 'source': {'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}, 'owner': {'flickrid': 'Fried Camels', 'name': 'Jinky the Fruit Bat'}, 'size': {'width': '353', 'height': '500', 'depth': '3'}}
aaa
{'folder': 'VOC2007', 'filename': '000001.jpg', 'source': {'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}, 'owner': {'flickrid': 'Fried Camels', 'name': 'Jinky the Fruit Bat'}, 'size': {'width': '353', 'height': '500', 'depth': '3'}}
{'folder': 'VOC2007', 'filename': '000001.jpg', 'source': {'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}, 'owner': {'flickrid': 'Fried Camels', 'name': 'Jinky the Fruit Bat'}, 'size': {'width': '353', 'height': '500', 'depth': '3'}, 'segmented': '0'}
aaa
bbb
aaa
{}
{'name': 'dog'}
aaa
{'name': 'dog'}
{'name': 'dog', 'pose': 'Left'}
aaa
{'name': 'dog', 'pose': 'Left'}
{'name': 'dog', 'pose': 'Left', 'truncated': '1'}
aaa
{'name': 'dog', 'pose': 'Left', 'truncated': '1'}
{'name': 'dog', 'pose': 'Left', 'truncated': '1', 'difficult': '0'}
aaa
bbb
aaa
{}
{'xmin': '48'}
aaa
{'xmin': '48'}
{'xmin': '48', 'ymin': '240'}
aaa
{'xmin': '48', 'ymin': '240'}
{'xmin': '48', 'ymin': '240', 'xmax': '195'}
aaa
{'xmin': '48', 'ymin': '240', 'xmax': '195'}
{'xmin': '48', 'ymin': '240', 'xmax': '195', 'ymax': '371'}
{'name': 'dog', 'pose': 'Left', 'truncated': '1', 'difficult': '0'}
{'name': 'dog', 'pose': 'Left', 'truncated': '1', 'difficult': '0', 'bndbox': {'xmin': '48', 'ymin': '240', 'xmax': '195', 'ymax': '371'}}
{'folder': 'VOC2007', 'filename': '000001.jpg', 'source': {'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}, 'owner': {'flickrid': 'Fried Camels', 'name': 'Jinky the Fruit Bat'}, 'size': {'width': '353', 'height': '500', 'depth': '3'}, 'segmented': '0'}
{'folder': 'VOC2007', 'filename': '000001.jpg', 'source': {'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}, 'owner': {'flickrid': 'Fried Camels', 'name': 'Jinky the Fruit Bat'}, 'size': {'width': '353', 'height': '500', 'depth': '3'}, 'segmented': '0', 'object': {'name': 'dog', 'pose': 'Left', 'truncated': '1', 'difficult': '0', 'bndbox': {'xmin': '48', 'ymin': '240', 'xmax': '195', 'ymax': '371'}}}
aaa
bbb
aaa
{}
{'name': 'person'}
aaa
{'name': 'person'}
{'name': 'person', 'pose': 'Left'}
aaa
{'name': 'person', 'pose': 'Left'}
{'name': 'person', 'pose': 'Left', 'truncated': '1'}
aaa
{'name': 'person', 'pose': 'Left', 'truncated': '1'}
{'name': 'person', 'pose': 'Left', 'truncated': '1', 'difficult': '0'}
aaa
bbb
aaa
{}
{'xmin': '8'}
aaa
{'xmin': '8'}
{'xmin': '8', 'ymin': '12'}
aaa
{'xmin': '8', 'ymin': '12'}
{'xmin': '8', 'ymin': '12', 'xmax': '352'}
aaa
{'xmin': '8', 'ymin': '12', 'xmax': '352'}
{'xmin': '8', 'ymin': '12', 'xmax': '352', 'ymax': '498'}
{'name': 'person', 'pose': 'Left', 'truncated': '1', 'difficult': '0'}
{'name': 'person', 'pose': 'Left', 'truncated': '1', 'difficult': '0', 'bndbox': {'xmin': '8', 'ymin': '12', 'xmax': '352', 'ymax': '498'}}
{'folder': 'VOC2007', 'filename': '000001.jpg', 'source': {'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}, 'owner': {'flickrid': 'Fried Camels', 'name': 'Jinky the Fruit Bat'}, 'size': {'width': '353', 'height': '500', 'depth': '3'}, 'segmented': '0', 'object': {'name': 'dog', 'pose': 'Left', 'truncated': '1', 'difficult': '0', 'bndbox': {'xmin': '48', 'ymin': '240', 'xmax': '195', 'ymax': '371'}}}
{'folder': 'VOC2007', 'filename': '000001.jpg', 'source': {'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}, 'owner': {'flickrid': 'Fried Camels', 'name': 'Jinky the Fruit Bat'}, 'size': {'width': '353', 'height': '500', 'depth': '3'}, 'segmented': '0', 'object': {'name': 'person', 'pose': 'Left', 'truncated': '1', 'difficult': '0', 'bndbox': {'xmin': '8', 'ymin': '12', 'xmax': '352', 'ymax': '498'}}}
{'folder': 'VOC2007', 'filename': '000001.jpg', 'source': {'database': 'The VOC2007 Database', 'annotation': 'PASCAL VOC2007', 'image': 'flickr', 'flickrid': '341012865'}, 'owner': {'flickrid': 'Fried Camels', 'name': 'Jinky the Fruit Bat'}, 'size': {'width': '353', 'height': '500', 'depth': '3'}, 'segmented': '0', 'object': {'name': 'person', 'pose': 'Left', 'truncated': '1', 'difficult': '0', 'bndbox': {'xmin': '8', 'ymin': '12', 'xmax': '352', 'ymax': '498'}}}

注意，for循环相当于遍历同一层节点，比如这里就是：<folder>，<filename>，<source>，<owner>等

  • 当<folder>遍历完之后，没有孩子节点了，因此回溯，注意此时是回溯到for循环下面（print(“aaa”)的地方），此时result是<folder>遍历完之后的值，因为result是在for循环外面定义的，同理<filename>也是

  • 当走到<source>的时候，他有子孩子，这个时候就会递归调用function，这个时候result就为空了，当这个for循环执行完之后，*有一个return，他会把result返回到<source>入口处，就是子孩子的result作为返回值给了父节点<source>

  • child_result = parse_xml_to_dict(child) # 递归遍历标签信息

  • child_result就存了子孩子的result,同时result恢复为父节点的result

Author: Moule Lin
Link: https://moulelin.github.io/2023/02/11/%E5%9B%9E%E6%BA%AF%E7%9A%84%E5%8F%98%E9%87%8F%E5%8F%98%E5%8C%96/
Reprint policy: All articles in this blog are used except for special statements CC BY 4.0 reprint polocy. If reproduced, please indicate source Moule Lin !
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