How do I determine the frequency of a .wav file in Python?

I am using Sox (sound eXchange)to record for 2 seconds as a .wav file in Python via the os module. I need to determine the frequency, in hertz, or average frequency of the file and save it to string. I cannot use software such as Audacity for this reason. I have tried using script from every related question off stack overflow, but have come up with nothing. Please help, I have spent countless hours trying to do this.