It's been a while since I've played with the Flickr API and I was pleasantly surprised by how much easier it's gotten to use. I don't believe the REST interface was available last time I tried (although it's possible I was just dumb and missed it) so I ended up using somebody's PHP XML-RPC class which was a bit clunky.

The REST API is dead-simple to use. The basic url format is

  http://api.flickr.com/services/rest/?method=<method-name>&name=value...

While only some API calls require authentication, all require an API key.

Here's what a call to flickr.photos.search method might look like:

  http://api.flickr.com/services/rest/?method=flickr.photos.search&api_key=YOURKEY&tags=monkey

The above call returns the 100 most recently uploaded photos matching the tag monkey. The flickr.photos.search method has lots of other options that let you customize the search.

You get back a big chunk of XML (there's a parameter to return JSON and several other formats instead) that looks like this:

<rsp stat="ok">    <photos page="1" pages="3410" perpage="100" total="340901">        <photo id="4195976808" owner="40592053@N02" secret="7605f0aa9f" server="2698" farm="3" title="373" ispublic="1" isfriend="0" isfamily="0"/>        <photo id="4195224913" owner="32143071@N00" secret="199a3c18cb" server="2650" farm="3" title="Q & Milk II" ispublic="1" isfriend="0" isfamily="0"/>    </photos></rsp>

Once you have a photo id, you can call flickr.photos.getinfo which, among other things, lets you get the URL to the page for that photo. You can also get thumbnail URLs in different sizes with a call to flickr.photos.getSizes.

I decided to do my latest playing around in Python rather than PHP. Here's a very basic function I threw together for making API calls:

def flickrRequest(method, params):    args = '&' + '&'.join([key + '=' + str(params[key]) for key in params.keys()])    url = "http://api.flickr.com/services/rest/?method=" + method + args    resp = urllib2.urlopen(url)    raw_xml = unicode(resp.read(), errors="ignore")    return minidom.parseString(raw_xml.encode("utf-8"))

It takes an API method name a dictionary of parameters, then uses urllib2 to get the XML response. The XML response is parsed using minidom and the DOM object is returned.

Since this is just for fun, the code basically just glosses over the Unicode aspect of the response by ignoring any Unicode errors. This lets us parse the XML at the expense of possible mangling some characters (generally only in the image title).

This is how the above function would be used to do a simple search:

tags = ["monkey", "chimp"]searchParams = {                    'api_key': FLICKR_API_KEY,                    'tags': ','.join(tags),                    'tag_mode': 'any',                    'content_type': 1,                    'page': 1                    'sort': 'date-posted-desc',                    }dom = flickrRequest('flickr.photos.search', searchParams)

This searches for any pictures that are tagged monkey or chimp. This only returns the first page (the first 100 by default). You can get the next batch by incrementing the page parameter.

Now let's say I want to call flickr.photos.getInfo for each image:

#This gives me all of the 'photo' nodes in the XMLphotos = dom.getElementsByTagName("photo")for photo in photos:  dom = flickrRequest('flickr.photos.getInfo', {'api_key': FLICKR_API_KEY, 'photo_id': photo.attributes["id"].value})  #The dom object now contains XML with info about the current photo  #You can take a look at the format here:  http://www.flickr.com/services/api/flickr.photos.getInfo.html

And that's the basics of using the Flickr REST api. My ultimate goal with learning the API is to write some sort of script that will let me backup all of the meta-information (tags, sets, collections, descriptions) of my Flickr account.