Изменить записи в файле конфигурации

Вот скрипт на Python, который должен делать то, что вы хотите:

#!/usr/bin/env python
# -*- encoding: ascii -*-
"""insert_xml.py"""

import sys
from bs4 import BeautifulSoup as Soup

# Get the filename from the command-line
filename = sys.argv[1]

with open(filename, 'r') as xmlfile:

    # Parse the file
    soup = Soup(xmlfile.read(), "html.parser")

    # Search for "description" tags
    for element in soup.findAll("description"):

        # Check to see if the "media:content" element is missing
        if element and not element.find_next_sibling("media:content"):

            # If so, construct a new "media:content" tag
            new_tag = soup.new_tag('media:content')
            new_tag["url"] = filename
            new_tag["type"] = "video/mpg"
            new_tag["expression"] = "full"

            # Insert the "media:content" tag after the "description" tag
            element.insert_after(new_tag)

    # Print the modified XML document - one element per line
    for element in soup.findAll():
        print(element)

Вот как это выглядит в действии:

$ python insert_xml.py in.xml

<description>Entrepreneur James overcame unconscionable childhood abuse before the sins of his past came back to haunt him.</description>
<media:content expression="full" type="video/mpg" url="in.xml"></media:content>
<media:rating>TV-14</media:rating>