Does Google appengine cache external requests?

I have a very simple application running on appengine that requests a web page every five minutes and parses for a specific piece of data.

Everything works fine except that the response I get back from the external request (using urllib2) doesn't reflect the latest changes to the page. Sometimes it takes a few minutes to get the latest, sometimes over an hour.

Is there a transparent layer of caching that appengine puts in place? Or is there something else I am missing here? I've looked at the caching headers of the requested page and there is no Expires, LastModified or ETags headers sent.

Update: Sometimes, it will get the new version of the pag开发者_JS百科e for a number of requests and then randomly later get an old out of date version.

It appears that this is an issue the App Engine team is aware of. The suggested workaround is to set Cache-Control header with max-age in seconds:

result = urlfetch.fetch(url, headers = {'Cache-Control' : 'max-age=240'})

should hopefully work for you.