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Hand coding an RSS 2.0 feed in Python

October 9, 2019

One requirement I have for tumblelog is that everything the Python version generates is identical to everything the Perl version generates. This means that sometimes I have to hand code a function that is available in a library for, say Python, but works differently in a Perl library.

When I was working on adding an RSS feed to Python version I decided to use lxml.etree as this would give me some control over the output. But, alas, not enough to match the output of the Perl version of tumblelog. Moreover, I was not really happy with the generated XML. So I decided to hand code both the Python and the Perl version.

def create_rss_feed(days, config):

    items = []
    todo = config['days']

    for day in days:
        (url, title, description) = get_url_title_description(day, config)

        end_of_day = get_end_of_day(day['date'])
        pub_date = end_of_day.strftime('%a, %d %b %Y %H:%M:%S %z')

        items.append(
            ''.join([
                '<item>'
                '<title>', escape(title), '</title>'
                '<link>', escape(url), '</link>'
                '<guid isPermaLink="true">', escape(url), '</guid>'
                '<pubDate>', escape(pub_date), '</pubDate>'
                '<description>', escape(description), '</description>'
                '</item>'
            ])
        )
        todo -= 1
        if not todo:
            break


    xml = ''.join([
        '<?xml version="1.0" encoding="UTF-8"?>'
        '<rss version="2.0" xmlns:atom="http://www.w3.org/2005/Atom">'
        '<channel>'
        '<title>', escape(config['name']), '</title>'
        '<link>', escape(config['blog-url']), '</link>'
        '<description>', escape(config['description']),'</description>'
        '<atom:link href="', escape(config['rss-feed-url']),
        '" rel="self" type="application/rss+xml" />',
        *items,
        '</channel>'
        '</rss>'
    ])
    feed_path = config['rss-path']
    p = Path(config['output-dir']).joinpath(feed_path)
    with p.open(mode='w', encoding='utf-8') as f:
        print(xml, file=f)

    if not config['quiet']:
        print(f"Created '{feed_path}'")

Note: if you think there are commas missing in the above code recall that in Python the compiler glues strings together if there is no comma between them.

Note: '<title>', escape(title), '</title>' can also be written as: 'f<title>{escape(title)}</title>' but I was afraid that this would make the code harder to read.

The code is quite straightforward. The calculation of the publication date is explained in RFC #822 and RFC #3339 dates in Python.

The escape function is imported from the html module.

If you are interested in the rest of the source code you can download it from GitHub.

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