如何使用lxml高效地解析这个包含嵌套元素的巨大XML文件？

Question

我尝试使用XML minidom解析这个巨大的XML文档。虽然它在一个示例文件上运行得很好，但在尝试处理实际文件（大约400MB）时，它阻塞了系统。在

我尝试从codereview调整代码（它以流方式处理数据，而不是一次在内存中加载数据），对于我的xml文件，由于元素的嵌套性质，我很难隔离数据集。我以前处理过简单的XML文件，但没有处理像这样的内存密集型任务。在

这是正确的方法吗？ 如何将库存和出版商标识与每本书相关联？这就是我计划最终将这两个表关联起来的方式。在

如有任何反馈，我们将不胜感激。在

在图书.xml在

<BookDatabase>
    <BookHeader>
        <Name>BookData</Name>
        <BookUniverse>All</BookUniverse>
        <AsOfDate>2010-05-02</AsOfDate>
        <Version>1.1</Version>
    </BookHeader>

    <InventoryBody>
        <Inventory ID="12">
            <PublisherClass ID="34">
                <Publisher>
                    <PublisherDetails>
                        <Name>Microsoft Press</Name>
                        <Type>Tech</Type>
                        <ID>7462</ID>
                    </PublisherDetails>
                </Publisher>
            </PublisherClass>
            <BookList>
                <Listing>
                    <BookListSummary>
                        <Date>2009-01-30</Date>
                    </BookListSummary>
                    <Book>
                        <BookDetail ID="67">
                            <BookName>Code Complete 2</BookName>
                            <Author>Steve McConnell</Author>
                            <Pages>960</Pages>
                            <ISBN>0735619670</ISBN>
                        </BookDetail>
                        <BookDetail ID="78">
                            <BookName>Application Architecture Guide 2</BookName>
                            <Author>Microsoft Team</Author>
                            <Pages>496</Pages>
                            <ISBN>073562710X</ISBN>
                        </BookDetail>
                    </Book>
                </Listing>
            </BookList>
        </Inventory>
        <Inventory ID="64">
            <PublisherClass ID="154">
                <Publisher>
                    <PublisherDetails>
                        <Name>O'Reilly Media</Name>
                        <Type>Tech</Type>
                        <ID>7484</ID>
                    </PublisherDetails>
                </Publisher>
            </PublisherClass>
            <BookList>
                <Listing>
                    <BookListSummary>
                        <Date>2009-03-30</Date>
                    </BookListSummary>
                    <Book>
                        <BookDetail ID="98">
                            <BookName>Head First Design Patterns</BookName>
                            <Author>Kathy Sierra</Author>
                            <Pages>688</Pages>
                            <ISBN>0596007124</ISBN>
                        </BookDetail>
                    </Book>
                </Listing>
            </BookList>
        </Inventory>
    </InventoryBody>
</BookDatabase>

Python代码：

^{pr2}$

Python输出：

$ python lxmletree_book.py 
========> 0 <=======
========> 1 <=======
{'ID': '12', 'element': 'Inventory'} []
========> 2 <=======
{'ID': '34', 'element': 'PublisherClass'} []
========> 3 <=======
{'Name': <Element Name at 0x105140af0>, 'Type': <Element Type at 0x105140b40>, 'ID': <Element ID at 0x105140b90>, 'element': 'PublisherDetails'} []
========> 4 <=======
{'ID': None, 'element': 'PublisherDetails'} []
========> 5 <=======
{'ID': None, 'element': 'PublisherClass'} []
========> 6 <=======
{'ISBN': <Element ISBN at 0x105140eb0>, 'Name': <Element Name at 0x105140dc0>, 'Author': <Element Author at 0x105140e10>, 'ID': '67', 'element': 'BookDetail', 'Pages': <Element Pages at 0x105140e60>} []
========> 7 <=======
{'ID': None, 'element': 'BookDetail'} []
========> 8 <=======
{'ISBN': <Element ISBN at 0x1051460a0>, 'Name': <Element Name at 0x105140f50>, 'Author': <Element Author at 0x105140fa0>, 'ID': '78', 'element': 'BookDetail', 'Pages': <Element Pages at 0x105146050>} []
========> 9 <=======
{'ID': None, 'element': 'BookDetail'} []
========> 10 <=======
{'ID': None, 'element': 'Inventory'} []
========> 11 <=======
{'ID': '64', 'element': 'Inventory'} []
========> 12 <=======
{'ID': '154', 'element': 'PublisherClass'} []
========> 13 <=======
{'Name': <Element Name at 0x105146230>, 'Type': <Element Type at 0x105146280>, 'ID': <Element ID at 0x1051462d0>, 'element': 'PublisherDetails'} []
========> 14 <=======
{'ID': None, 'element': 'PublisherDetails'} []
========> 15 <=======
{'ID': None, 'element': 'PublisherClass'} []
========> 16 <=======
{'ISBN': <Element ISBN at 0x1051465f0>, 'Name': <Element Name at 0x105146500>, 'Author': <Element Author at 0x105146550>, 'ID': '98', 'element': 'BookDetail', 'Pages': <Element Pages at 0x1051465a0>} []
========> 17 <=======
{'ID': None, 'element': 'BookDetail'} []
========> 18 <=======
{'ID': None, 'element': 'Inventory'} []
========> 19 <=======

期望的输出（最终存储在MySQL中—现在是Python中的列表）：

Publishers
InventoryID PublisherClassID Name            Type ID
12          34               Microsoft Press Tech 7462
64          154              O'Reilly Media  Tech 7484

Books
PublisherID BookDetailID Name                              Author           Pages ISBN
7462        67           Code Complete 2                   Steve McConnell  960   0735619670
7462        78           Application Architecture Guide 2  Microsoft Team   496   073562710X
7484        98           Head First Design Patterns        Kathy Sierra     688   0596007124

Answer 1

你可以试试这样的方法：

import MySQLdb
from lxml import etree
import config

def fast_iter(context, func, args=[], kwargs={}):
    # http://www.ibm.com/developerworks/xml/library/x-hiperfparse/
    # Author: Liza Daly    
    for event, elem in context:
        func(elem, *args, **kwargs)
        elem.clear()
        while elem.getprevious() is not None:
            del elem.getparent()[0]
    del context

def extract_paper_elements(element,cursor):
    pub={}        
    pub['InventoryID']=element.attrib['ID']
    try:
        pub['PublisherClassID']=element.xpath('PublisherClass/@ID')[0]
    except IndexError:
        pub['PublisherClassID']=None
    pub['PublisherClassID']=element.xpath('PublisherClass/@ID')[0]
    for key in ('Name','Type','ID'):
        try:
            pub[key]=element.xpath(
                'PublisherClass/Publisher/PublisherDetails/{k}/text()'.format(k=key))[0]
        except IndexError:
            pub[key]=None
    sql='''INSERT INTO Publishers (InventoryID, PublisherClassID, Name, Type, ID)
           VALUES (%s, %s, %s, %s, %s)
        '''
    args=[pub.get(key) for key in
          ('InventoryID', 'PublisherClassID', 'Name', 'Type', 'ID')]
    print(args)
    # cursor.execute(sql,args)
    for bookdetail in element.xpath('descendant::BookList/Listing/Book/BookDetail'):
        pub['BookDetailID']=bookdetail.attrib['ID']
        for key in ('BookName', 'Author', 'Pages', 'ISBN'):
            try:
                pub[key]=bookdetail.xpath('{k}/text()'.format(k=key))[0]
            except IndexError:
                pub[key]=None
        sql='''INSERT INTO Books
               (PublisherID, BookDetailID, Name, Author, Pages, ISBN)
               VALUES (%s, %s, %s, %s, %s, %s)
            '''           
        args=[pub.get(key) for key in
              ('ID', 'BookDetailID', 'BookName', 'Author', 'Pages', 'ISBN')]
        # cursor.execute(sql,args)
        print(args)


def main():
    context = etree.iterparse("book.xml", events=("end",), tag='Inventory')
    connection=MySQLdb.connect(
        host=config.HOST,user=config.USER,
        passwd=config.PASS,db=config.MYDB)
    cursor=connection.cursor()

    fast_iter(context,extract_paper_elements,args=(cursor,))

    cursor.close()
    connection.commit()
    connection.close()

if __name__ == '__main__':
    main()

1. 不要使用fast_iter2。original ^{}分隔 来自特定处理函数的有用工具 （extract_paper_elements）。fast_iter2将两者混合在一起 没有可重复的代码。在
2. 如果在etree.iterparse("book.xml", events=("end",), tag='Inventory')中设置tag参数，则处理函数 extract_paper_elements将只看到Inventory元素。在
3. 给定一个Inventory元素，您可以使用xpath方法进行挖掘 把所需的数据收集下来。在
4. args和kwargs参数被添加到fast_iter所以cursor 可以传递给extract_paper_elements。在