I could not understand the def function in this piece of code-CodePudding

I can't understand what is lookup function doing

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

This is the full piece of code, also if you need to find the Library.xml file, you can go to this link to see for more context : https://www.py4e.com/code3.zip to download the zip file and then you can go to the tracks file to find the library.xml file. Really appreciate if anyone could help me

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()

CodePudding user response：

That function could use a doc string! If you look at the child XML elements under <dict>, you'll see entries like

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

So, key/value pairs are actually 2 sibling elements, one right after the other. The second element tag name is hard to guess because it encodes the type (string / integer / etc). That makes it hard to search for. But you know its the very next element and that's what the loop does. When the loop finds an element with the text you want, it sets found = True. The next round of the loop is the element with the value you want.

If the loop doesn't find the text you want, it exits and you then return None.