Help: Switching usrp to capture different frequencies alternately using python thread

Hi everyone ,
I have been trying an experiment in trying to capture different
using python thread to alternately capture different frequencies.
what i am trying is like this [ pseudo code ].
#freq_list = [ ‘222’,‘787’]
1: capture 222 using… by supplying freq = 222 to
2: wait for 2 min and let frequency 222 to be used for capturing data
3; Now switch to frequency 787 and start capturing data, by simply
changing the frequency parameter to
4 … and the loop goes on.

I am using python thread to switch the frequencies to

But i am not able to get the required output… can someone help me in
explaining how does usrp reacts when a frequency is fed to

to capture data.I am confused why my experiment is not working.
Please tolerate me if i have post with mistakes…