adding error handling to send method

[btoews]

There is no good way of catching or dealing with exceptions that are raised during the request sending process when using map or imap. For example, I am writing a script to test it webservers are up. If a ConnectionError is raised I wouldn't be able to do anything about it. This commit adds an exception_handler parameter to the map,imap, and send methods. This callback gets called with the request and exception in the event of an exception being raised.

I do this with gevent.greenlet.Greenlet.link_exception, but I am not sure that this is the best way of doing it. It would be nice if there was a way to catch exceptions rather than just linking to them. Have you thought about catching ConnectionError in requests and adjusting the response.error and whatnot accordingly?

Here is an example use-case:

import grequests

def eh(request,exception):
    print "couldn't request %s because of exception: %s" % (request.url,exception.__class__.__name__)

req  = grequests.get('http://127.0.0.1:123')
res  = grequests.map([req],exception_handler=eh)

[piotr-dobrogost]

Somehow related #6

[kennethreitz]

Hmm, this is an interesting approach.

[btoews]

better addressed by #22