import Cookie
c = Cookie.SimpleCookie()
c.load('__atrfs={"dr":"http://example.org/?id=1"')


# I solved removing the add this cookies from the string before parsing
# It's an ugly hack but seems to work.
def sanitizeCookie(aCookie):
    c = re.sub('\s?__atuvc.*?;', '', aCookie)
    c = re.sub('\s?__at.*?};?', '', c)
    return re.sub('\s?_at.*?};?', '', c)

#then call 
c.load(sanitizeCookie(cooakieString))