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Parsing XML Documents with Python

XML is the return format for many APIs. It is likely you will work with it in your career. Python is an excellent language for parsing and writing XML to interact with these APIs and other circumstances you may encounter. In this lab we will use Python's `defusedxml` package to write an XML file, allow the intended user to make use of the XML and make changes, and then parse the XML for the changes. You will need basic Python programming and SQL skills for this lab: - [Certified Associate in Python Programming Certification](

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Path Info

Clock icon Beginner
Clock icon 1h 0m
Clock icon Jun 05, 2020

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Table of Contents

  1. Challenge

    Write an XML File contains a skeleton of what we need for this objective. Run it to see that it returns an error:


    The example code showing how to make this work is shown below:

    import sqlite3
    import xml.etree.ElementTree as ET
    from xml.etree.ElementTree import Element, ElementTree
    DB_NAME = "author_contracts.db"
    def get_db_data():
        write a code to execute the sql script and return the results
        sql_query = """SELECT author, title, genre FROM authors"""
        con = sqlite3.connect(DB_NAME)
        cur = con.cursor()
        results = cur.fetchall()
        return results
    def create_book_entry(author, title, genre):
        create the book entry as defined and return book
        book = Element('book')
        author_tag = ET.SubElement(book, 'author')
        author_tag.text = author
        title_tag = ET.SubElement(book, 'title')
        title_tag.text = title
        genre_tag = ET.SubElement(book, 'genre')
        genre_tag.text = genre
        ET.SubElement(book, 'isbn')
        return book
    # using the information from get_db_data()
    # write code to create a root and then
    # add each book to it, finally write
    # data to "catalog.xml"
    root = Element("catalog")
    book_info = get_db_data()
    for author, title, genre in book_info:
        book = create_book_entry(author, title, genre)
    tree = ElementTree(element=root)
    tree.write("catalog.xml", encoding="UTF-8", xml_declaration=True)
    # test code
    expected_catalog = b"<?xml version='1.0' encoding='UTF-8'?>\n<catalog><book><author>Thompson, Keith</author><title>Oh Python! My Python!</title><genre>biography</genre><isbn /></book><book><author>Fritts, Larry</author><title>Fun with Django</title><genre>satire</genre><isbn /></book><book><author>Applegate, John</author><title>When Bees Attack! The Horror!</title><genre>horror</genre><isbn /></book><book><author>Brown, James</author><title>Martin Buber's Philosophies</title><genre>guide</genre><isbn /></book><book><author>Smith, Jackson</author><title>The Sun Also Orbits</title><genre>mystery</genre><isbn /></book></catalog>"
        with open("catalog.xml", "rb") as f:
            catalog =
    except FileNotFoundError:
        catalog = ""
    assert catalog == expected_catalog

    Run python

    Congratulations! The data is in a format the ISBN company can use.

  2. Challenge

    Parse XML Changes

    First install defusedxml:

    pip3 install defusedxml

    Then we can work on It contains a skeleton of what we need for this next objective. Run python before editing, to see that it returns an error.

    The example code showing how to accomplish this second objective is shown below:

    import sqlite3
    import sys
    import defusedxml.ElementTree as ET
    DB_NAME = "author_contracts.db"
    def update_db(isbn_data_list):
        add code to execute each sql_stmt in the order given
        results from sql_query_3 should be assigned to results
        sql_query_1 = ''' ALTER TABLE authors ADD COLUMN isbn CHAR(20); '''
        sql_query_2 = "UPDATE authors SET isbn = ? WHERE title = ?;"
        sql_query_3 = ''' SELECT isbn FROM authors;'''
        con = sqlite3.connect("DB_NAME")
        cur = con.cursor()
        con.executemany(sql_query_2, isbn_data_list)
        results = cur.fetchall()
        # test code
        expected_results = [('000-1-000000-00-1',), ('000-2-000000-00-2',), ('000-3-000000-00-3',), ('000-4-000000-00-4',), ('000-5-000000-00-5',)]
        assert results == expected_results
    # using 'isbn.xml'
    # loop through "book" in file and append isbn and title as a list object to isbn_data_list
    # send isbn_data_list to function update_db
    file_name = "isbn.xml"
        tree = ET.parse(file_name)
        print("File not found")
    isbn_data_list = []
    for book in tree.findall('book'):
        title = book.findtext('title')
        isbn = book.findtext('isbn')
        isbn_data_list.append([isbn, title])

    Now run python

    Awesome! You have mastered XML file parsing.

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