此功能如何在XML树工作中搜索节点？

Question

我无法理解什么是查找功能在做什么

def lookup(d, key):
    found = False
    for child in d:
        if found : return child.text
        if child.tag == 'key' and child.text == key :
            found = True
    return None

这是完整的代码，同样，如果您需要查找library.xml文件，则可以转到此链接以查看更多上下文：

Https：//www.py4e.com/code4.com/code3.zip

下载zip文件，然后可以转到曲目文件以查找库库文件。

import xml.etree.ElementTree as ET
import sqlite3

conn = sqlite3.connect('trackdb.sqlite')
cur = conn.cursor()

# Make some fresh tables using executescript()
cur.executescript('''
DROP TABLE IF EXISTS Artist;
DROP TABLE IF EXISTS Album;
DROP TABLE IF EXISTS Track;

CREATE TABLE Artist (
    id  INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
    name    TEXT UNIQUE
);

CREATE TABLE Album (
    id  INTEGER NOT NULL PRIMARY KEY AUTOINCREMENT UNIQUE,
    artist_id  INTEGER,
    title   TEXT UNIQUE
);

CREATE TABLE Track (
    id  INTEGER NOT NULL PRIMARY KEY 
        AUTOINCREMENT UNIQUE,
    title TEXT  UNIQUE,
    album_id  INTEGER,
    len INTEGER, rating INTEGER, count INTEGER
);
''')


fname = input('Enter file name: ')
if ( len(fname) < 1 ) : fname = 'Library.xml'

# <key>Track ID</key><integer>369</integer>
# <key>Name</key><string>Another One Bites The Dust</string>
# <key>Artist</key><string>Queen</string>
def lookup(d, key):
    found = False
    for child in d:
        if found : return child.text
        if child.tag == 'key' and child.text == key :
            found = True
    return None

stuff = ET.parse(fname)
all = stuff.findall('dict/dict/dict')
print('Dict count:', len(all))
for entry in all:
    if ( lookup(entry, 'Track ID') is None ) : continue

    name = lookup(entry, 'Name')
    artist = lookup(entry, 'Artist')
    album = lookup(entry, 'Album')
    count = lookup(entry, 'Play Count')
    rating = lookup(entry, 'Rating')
    length = lookup(entry, 'Total Time')

    if name is None or artist is None or album is None : 
        continue

    print(name, artist, album, count, rating, length)

    cur.execute('''INSERT OR IGNORE INTO Artist (name) 
        VALUES ( ? )''', ( artist, ) )
    cur.execute('SELECT id FROM Artist WHERE name = ? ', (artist, ))
    artist_id = cur.fetchone()[0]

    cur.execute('''INSERT OR IGNORE INTO Album (title, artist_id) 
        VALUES ( ?, ? )''', ( album, artist_id ) )
    cur.execute('SELECT id FROM Album WHERE title = ? ', (album, ))
    album_id = cur.fetchone()[0]

    cur.execute('''INSERT OR REPLACE INTO Track
        (title, album_id, len, rating, count) 
        VALUES ( ?, ?, ?, ?, ? )''', 
        ( name, album_id, length, rating, count ) )

    conn.commit()

功能可以使用DOC字符串！如果您查看the的孩子XML元素，您会看到类似的条目

Answer 1

<dict>

SO，键/值对实际上是2个同级元素，一个接一个。第二个元素标签名称很难猜测，因为它编码类型（String / Integer / etc）。这使得很难搜索。但是您知道这是下一个元素，这就是循环的作用。当循环找到带有所需文本的元素时，它会设置

<key>Track ID</key><integer>369</integer>
<key>Name</key><string>Another One Bites The Dust</string>

。循环的

next

圆形是带有您想要的值的元素。

如果循环找不到您想要的文本，它将退出，然后您返回

found = True

。