Python equivalent of Common Lisp Macros?

Chris Rebert clp at rebertia.com
Wed Nov 26 20:30:02 CET 2008


On Wed, Nov 26, 2008 at 11:13 AM, dpapathanasiou
<denis.papathanasiou at gmail.com> wrote:
> I'm using the feedparser library to extract data from rss feed items.
>
> After I wrote this function, which returns a list of item titles, I
> noticed that most item attributes would be retrieved the same way,
> i.e., the function would look exactly the same, except for the single
> data.append line inside the for loop.
>
> In CL, I could simply write a macro, then replace the data.append line
> depending on which attribute I wanted.
>
> Is there anything similar in Python?

Yes, use higher-order functions. See below.

>
> Here's the function:
>
> def item_titles (feed_url):
Replace previous line with:
def item_titles(feed_url, attr_getter):
>    """Return a list of the item titles found in this feed url"""
>    data = []
>    feed = feedparser.parse(feed_url)
>    if feed:
>        if len(feed.version) > 0:
>            for e in feed.entries:
>                data.append(e.title.encode('utf-8'))
Replace previous line with:
                data.append(attr_getter(e))
>    return data

Example usage:

def title_getter(entry):
    return entry.title.encode('utf-8')

titles = item_titles("some feed url here", title_getter)

As I'm not familiar with feedparser, you might want to move where the
.encode() takes place, but you get the idea.

Cheers,
Chris
-- 
Follow the path of the Iguana...
http://rebertia.com

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