requests python session with change headers

s = requests.Session()

if not os.path.exists("templates"):
    os.makedirs("templates")
    for i in dict_accounts.keys():
        os.makedirs("templates/%s" % i)

for key,val in dict_accounts.iteritems():
    print key
    urlfinal = "https:urlmaneira"
    r = s.get(urlfinal, verify=False,stream=True,headers={'User-Agent':"Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:26.0) Gecko/20100101 Firefox/26.0"})
    print urlfinal
    print r.request.headers
    print r.text
    break