I have created simple code allowing me to use the urJTAG from the Python code.
It was tailored for controlling of the Xilinx FPGAs vie the BSCAN_SPARTAN3 component.
I've checked it with the embedded USB cable included in SPARTAN-3E Starter Kit, but it
should also work with other cables supported by urJTAG.
Unfortunately this code runs urJTAG interactively via Python's "pexpect" module, and therefore
it is awfully slow :-(.
The possibility of calling urJTAG directly probably could spped it significantly up.
If someone is interested in my solution - here is the code:
And here is a discussion, which lead me to write it: