sphinx could not understand audio speech recognition

1#!/usr/env/python3
2import speech_recognition as sr
3
4r = sr.Recognizer()
5m = sr.Microphone()
6
7try:
8    print("A moment of silence, please...")
9    with m as source: r.adjust_for_ambient_noise(source)
10    print("Set minimum energy threshold to {}".format(r.energy_threshold))
11    while True:
12        print("Say something!")
13        with m as source: audio = r.listen(source)
14        print("Got it! Now to recognize it...")
15        try:
16            value = r.recognize_google(audio)
17
18            if str is bytes:
19                print(u"You said {}".format(value).encode("utf-8"))
20            else:
21                print("You said {}".format(value))
22        except sr.UnknownValueError:
23            print("Oops! Didn't catch that")
24        except sr.RequestError as e:
25            print("Uh oh! Couldn't request results from Google Speech Recognition service; {0}".format(e))
26except KeyboardInterrupt:
27    pass