How to modify content using DOM in XML

How to modify an XML document using DOM in Python? Use minidom to parse XML files as DOM trees. Get the target node to be modified. Use the firstChild property to modify the node text content. Write to the modified XML file. Free up memory to avoid leakage.

XML DOM modification: In-depth analysis and practical skills

Have you ever thought about how to efficiently modify the content of an XML document? Directly modifying XML files with a text editor is not only time-consuming and labor-intensive, but also prone to errors, resulting in the failure of the XML structure. At this time, the DOM (Document Object Model) comes in handy. This article will explore in-depth how to use DOM to modify XML content, and share some problems and solutions encountered in actual applications. After reading this article, you will master the essence of DOM modifying XML and be able to write efficient and robust code.

First, we need to clarify the essence of DOM: it parses the XML document into a tree structure, which makes it easier for us to access and operate each node programmatically. This is like dismantling a big tree into branches and leaves, and we can modify, add or delete these components at will. Python's xml.dom.minidom module provides such capabilities.

Let's look at a simple example, suppose we want to modify a simple XML file:

 <code class="xml"><bookstore> <book category="cooking"> <title lang="en">Everyday Italian</title> <author>Giada De Laurentiis</author> <year>2005</year> <price>30.00</price> </book> <book category="children"> <title lang="en">Harry Potter</title> <author>J K. Rowling</author> <year>2005</year> <price>29.99</price> </book> </bookstore></code>

We hope to change the price of Everyday Italian to 35.00 . Using minidom , the code is as follows:

 <code class="python">from xml.dom.minidom import parse dom = parse("bookstore.xml") # 解析XML文件root = dom.documentElement # 获取根节点books = root.getElementsByTagName("book") # 获取所有book节点for book in books: if book.getElementsByTagName("title")[0].firstChild.data == "Everyday Italian": price_node = book.getElementsByTagName("price")[0] price_node.firstChild.data = "35.00" break # 找到目标节点后退出循环，提高效率with open("bookstore_modified.xml", "w") as f: dom.writexml(f, addindent=" ", newl="\n", encoding="utf-8") # 写入修改后的XML文件dom.unlink() # 释放内存，非常重要！</code>

This code clearly shows the process of DOM modifying XML: first parsing the XML file, then finding the target node (price node), modifying its text content, and finally writing the modified XML file. Pay attention to the last line dom.unlink() . This step is crucial. It frees up the memory occupied by the DOM tree to avoid memory leakage, especially when dealing with large XML files.

In advanced usage, you may encounter situations where you need to add or delete nodes. appendChild() and removeChild() methods are used to add and delete child nodes respectively. Remember that DOM operations are based on tree structures, and you need to clarify the parent-child relationship between nodes in order to correctly add or delete operations.

Problems that may be encountered: When dealing with large XML files, the DOM can consume a lot of memory. For super-large XML files, the SAX (Simple API for XML) parser is a better choice because it is an event-based parsing method with a lower memory footprint. However, SAX's programming model is more complex than DOM. Which parser to choose depends on your specific requirements and the size of the XML file.

In terms of performance optimization, try to minimize the number of traversals on the DOM tree. Rationally utilizing XPath expressions can improve the efficiency of finding target nodes. In addition, good programming habits, such as using meaningful variable names and adding necessary comments, can improve the readability and maintainability of the code. Remember, concise and efficient code is the pursuit of programmers.

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