SAGA has a command-line interface, so once you have it installed and on your system path, you can access the tools directly using a command line call from Python (I do this all the time with R, the process is very similar). Here's an example of calling the help function for SAGA:
from subprocess import call
and here's the help for the tool you want to use:
call(['saga_cmd', 'ta_preprocessor', '4'])
You should be able to figure out the sequence of arguments to build the full command from there. Note that all the processing happens outside of python, so you'll need to supply an *.sgrd file as input and the tool will write another one (or more) to disk.