Not sure if I undestand correctly, but I think you are referring to functions?
4. More Control Flow Tools — Python 3.5.2 documentation
So within a for loop you can call another function for each loop step to return a result e.g.
def myFunction( raster, val ):
newval = raster * val
return newval
for r in rasterlist:
rmod = myFunction(r, 3.14159265)