概述

自己在用labelImg打好标签后，想只用其中几类训练，不想训练全部类别，又不想重新打标生成.xml文件，因此想到这个办法：直接在.xml文件中删除原有的不需要的标签类及其属性。

打标时标签名出现了大小写（工程量大时可能会手滑），程序中有改写标签值为小写的过程，因为我做py-faster-rcnn 训练时，标签必须全部为小写。

以如下的.xml文件为例，我故意把标签增加了大写

<annotation verified="yes">
	<filename>test.jpg</filename>
	<path>C:\Users\yasin\Desktop\test</path>
	<source>
		<database>Unknown</database>
	</source>
	<size>
		<width>400</width>
		<height>300</height>
		<depth>3</depth>
	</size>
	<segmented>0</segmented>
	<object>
		<name>People</name>
		<pose>Unspecified</pose>
		<truncated>0</truncated>
		<difficult>0</difficult>
		<bndbox>
			<xmin>80</xmin>
			<ymin>69</ymin>
			<xmax>144</xmax>
			<ymax>89</ymax>
		</bndbox>
	</object>
	<object>
		<name>CAT</name>
		<pose>Unspecified</pose>
		<truncated>0</truncated>
		<difficult>0</difficult>
		<bndbox>
			<xmin>40</xmin>
			<ymin>69</ymin>
			<xmax>143</xmax>
			<ymax>16</ymax>
		</bndbox>
	</object>
	<object>
		<name>dog</name>
		<pose>Unspecified</pose>
		<truncated>0</truncated>
		<difficult>0</difficult>
		<bndbox>
			<xmin>96</xmin>
			<ymin>82</ymin>
			<xmax>176</xmax>
			<ymax>87</ymax>
		</bndbox>
	</object>	
</annotation>

具体实现

假如我们只想保留图片上的people和cat类，其他都删除，代码如下：

from xml.etree.ElementTree import ElementTree
from os import walk, path

def read_xml(in_path):
    tree = ElementTree()
    tree.parse(in_path)
    return tree

def write_xml(tree, out_path):
    tree.write(out_path, encoding="utf-8", xml_declaration=True)

def find_nodes(tree, path):
    return tree.findall(path)

def del_node_by_target_classes(nodelist, target_classes_lower, tree_root):
    for parent_node in nodelist:
        children = parent_node.getchildren()
        if (parent_node.tag == "object" and children[0].text.lower() not in target_classes_lower):
            tree_root.remove(parent_node)
        elif (parent_node.tag == "object" and children[0].text.lower() in target_classes_lower):
            children[0].text = children[0].text.lower()

def get_fileNames(rootdir):
    data_path = []
    prefixs = []
    for root, dirs, files in walk(rootdir, topdown=True):
        for name in files:
            pre, ending = path.splitext(name)
            if ending != ".xml":
                continue
            else:
                data_path.append(path.join(root, name))
                prefixs.append(pre)

    return data_path, prefixs

if __name__ == "__main__":
    # get all the xml paths, prefixes if not used here
    paths_xml, prefixs = get_fileNames("/home/yasin/old_labels/")

    target_classes = ["PEOPLE", "CAT"] # target flags you want to keep

    target_classes_lower = []
    for i in range(len(target_classes)):
        target_classes_lower.append(target_classes[i].lower()) # make sure your target is lowe-case

    # print(target_classes_lower)
    for i in range(len(paths_xml)):
        # rename and save the corresponding xml
        tree = read_xml(paths_xml[i])
        
        # get tree node
        tree_root = tree.getroot()

        # get parent nodes
        del_parent_nodes = find_nodes(tree, "./")
        
        # get target classes and delete
        target_del_node = del_node_by_target_classes(del_parent_nodes, target_classes_lower, tree_root)
        
        # save output xml, 000001.xml
        write_xml(tree, "/home/yasin/new_labels/{}.xml".format("%06d" % i))

按照上述代码，示例.xml变为如下.xml，可以看出我们删除了除people和cat类的类别（即dog类），并把保留类别的打标改成了小写：

<?xml version='1.0' encoding='utf-8'?>
<annotation verified="yes">
	<filename>test.jpg</filename>
	<path>C:\Users\yasin\Desktop\test</path>
	<source>
		<database>Unknown</database>
	</source>
	<size>
		<width>400</width>
		<height>300</height>
		<depth>3</depth>
	</size>
	<segmented>0</segmented>
	<object>
		<name>people</name>
		<pose>Unspecified</pose>
		<truncated>0</truncated>
		<difficult>0</difficult>
		<bndbox>
			<xmin>80</xmin>
			<ymin>69</ymin>
			<xmax>144</xmax>
			<ymax>89</ymax>
		</bndbox>
	</object>
	<object>
		<name>cat</name>
		<pose>Unspecified</pose>
		<truncated>0</truncated>
		<difficult>0</difficult>
		<bndbox>
			<xmin>40</xmin>
			<ymin>69</ymin>
			<xmax>143</xmax>
			<ymax>16</ymax>
		</bndbox>
	</object>
</annotation>