This question relates to python variable to R and perhaps also to this python objects to rpy2 but none of the two completely overlaps and the first one is actually unanswere
I'd recommend you to create an function, as the R function exposed by rpy2 can be called just as if it was a Python function.
my_func = robjects.r(''' function(strg) { test <- gsub("to", "",strg) test } ''') my_func(strg)