remove f-strings and one minor bug

* use username and password
* default to python3

fritzbox_helper.py

@@ -90,7 +90,7 @@ def calculate_pbkdf2_response(challenge, password):
     # Once with dynamic salt.
     hash1 = hashlib.pbkdf2_hmac("sha256", password.encode(), salt1, iter1)
     hash2 = hashlib.pbkdf2_hmac("sha256", hash1, salt2, iter2)
-    return f"{challenge_parts[4]}${hash2.hex()}"
+    return "{}${}".format(challenge_parts[4], hash2.hex())
 
 
 def calculate_md5_response(challenge, password):

fritzbox_traffic.py

@@ -36,11 +36,10 @@ def print_values():
     except Exception as e:
         sys.exit("Couldn't get WAN traffic")
 
-    traffic = fs.transmission_rate
+    down_traffic = fs.bytes_received
-    down_traffic = traffic[1]
     print("down.value %d" % down_traffic)
 
-    up_traffic = traffic[0]
+    up_traffic = fs.bytes_received
     print("up.value %d" % up_traffic)
 
     if not os.environ.get("traffic_remove_max"):