python利用lxml读写xml格式的文件

Python  /  管理员 发布于 7年前   390

之前在转换数据集格式的时候需要将json转换到xml文件，用lxml包进行操作非常方便。

1. 写xml文件

a) 用etree和objectify

from lxml import etree, objectifyE = objectify.ElementMaker(annotate=False)anno_tree = E.annotation(  E.folder('VOC2014_instance'),  E.filename("test.jpg"),  E.source(    E.database('COCO'),    E.annotation('COCO'),    E.image('COCO'),    E.url("http://test.jpg")  ),  E.size(    E.width(800),    E.height(600),    E.depth(3)  ),  E.segmented(0),)etree.ElementTree(anno_tree).write("text.xml", pretty_print=True)

输出的test.xml文件内容如下：

```

如果需要在anno_tree的基础上加其他标签的话用append即可:

E2 = objectify.ElementMaker(annotate=False)anno_tree2 = E2.object(  E.name("person"),  E.bndbox(    E.xmin(100),    E.ymin(200),    E.xmax(300),    E.ymax(400)  ),  E.difficult(0))anno_tree.append(anno_tree2)

上面的输出就变成了:

<annotation> <folder>VOC2014_instance/person</folder> <filename>test.jpg</filename> <source>  <database>COCO</database>  <annotation>COCO</annotation>  <image>COCO</image>  <url>http://test.jpg</url> </source> <size>  <width>800</width>  <height>600</height>  <depth>3</depth> </size> <segmented>0</segmented> <object>  <name>person</name>  <bndbox>   <xmin>100</xmin>   <ymin>200</ymin>   <xmax>300</xmax>   <ymax>400</ymax>  </bndbox>  <difficult>0</difficult> </object></annotation>

b) 用etree和SubElement

annotation = etree.Element("annotation")etree.SubElement(annotation, "folder").text = "VOC2014_instance"etree.SubElement(annotation, "filename").text = "test.jpg"source = etree.SubElement(annotation, "source")etree.SubElement(source, "database").text = "COCO"etree.SubElement(source, "annotation").text = "COCO"etree.SubElement(source, "image").text = "COCO"etree.SubElement(source, "url").text = "http://test.jpg"size = etree.SubElement(annotation, "size")etree.SubElement(size, "width").text ='800' # 必须用stringetree.SubElement(size, "height").text = '600'etree.SubElement(size, "depth").text = '3'etree.SubElement(annotation, "segmented").text = '0'key_object = etree.SubElement(annotation, "object")etree.SubElement(key_object, "name").text = “person”bndbox = etree.SubElement(key_object, "bndbox")etree.SubElement(bndbox, "xmin").text = str(100)etree.SubElement(bndbox, "ymin").text = str(200)etree.SubElement(bndbox, "xmax").text = str(300)etree.SubElement(bndbox, "ymax").text = str(400)etree.SubElement(key_object, "difficult").text = '0'doc = etree.ElementTree(annotation)doc.write(open("test.xml", "w"), pretty_print=True)

2. 读xml

这里可以用xpath直接提取所需的元素的值。比如想要获取上面test.xml文件的x, y坐标：

tree = etree.parse("test.xml")# get bboxfor bbox in tree.xpath('//bndbox'):  # 获取bndbox元素的内容  for corner in bbox.getchildren(): # 便利bndbox元素下的子元素    print corner.text  # string类型

参考

http://lxml.de/tutorial.html

https://stackoverflow.com/questions/12657043/parse-xml-with-lxml-extract-element-value

以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持。