This is a little piece of code I wrote to intercept and disregard a http or https request from urllib.urlopen if the Content-Type header on the response is not within a list of accepted content types.
I'm sure somebody might find a use for this.
This snippet creates a customer URLopener and then overrides the open_http and open_https methods, checks for MIME type and halts the request if the response is of a MIME type you do not accept.