def callback(track_transfer_batch, entry, dest, done, total, fraction, user_param1, ...)

Emitted regularly throughout the transfer to allow progress bars and other UI elements to be updated.

track_transfer_batch :

instance of RB.TrackTransferBatch that is emitting the signal

entry :

the RB.RhythmDBEntry being transferred

dest :

the destination URI for the transfer

done :

some measure of how much of the transfer is done

total :

the total amount of that same measure

fraction :

the fraction of the transfer that is done

user_param1 :

first user parameter (if any) specified with the connect() method

... :

additional user parameters (if any)