Yesterday I described how to record the IQ data from the USRP focusing on generating unique file names every time the GNU Radio / GRC script is executed. Playing the recorded IQ data is really simple: We take the corresponding receiver application and replace the USRP source with a file source and a throttle block.
I needed a quick USRP IQ data recorder today to record the APT downlink from NOAA satellites. This is really trivial to implement using the GNU Radio Companion, but I had to figure out how to use dynamic filenames to avoid overwriting previously recorded data. Of course, I could just rename each file when recording has finished but I am too lazy to do things like that. Using the current date and time in the file name seemed to be a good solution.
This quick how-to explains how to use the Python datetime module to generate a unique filename in GRC.