Something

#!/usr/bin/env python

import mechanize
import sys, logging, re

#logger = logging.getLogger("mechanize")
#logger.addHandler(logging.StreamHandler(sys.stdout))
#logger.setLevel(logging.DEBUG)
br = mechanize.Browser(factory=mechanize.DefaultFactory(i_want_broken_xhtml_support=True))
#br.set_debug_responses(True)
#br.set_debug_http(True)
br.open("http://pastebin.ca/upload.php")
print br.title()
br.select_form(nr=4)
br.form.add_file(open("pastebin.py"), "text/plain", "pastebin.py")
br.submit()
html = re.sub(r'[^ ]/>', r' />', br.response().get_data(), flags=re.DOTALL, count=0)
response = mechanize.make_response(html, [("Content-Type", "text/html")], "http://pastebin.ca/upload.php", 200, "OK")
br.set_response(response)
br.select_form(nr=4)
#br.form.set_value(["11"], name='type', kind="list")
#br.form.set_value(["5 minutes"],name='expiry', kind="list")
br.submit()
#print br.response().read()
print br.response().geturl()