R is to Python as Latin is to English. Sooner or later you will have to communicate with the rest of the world, and you're going to find your choice of Latin, while having a substantial use case, to not be sufficient for the purpose.
The Python programmers can probably step through R source code and figure out what's going on without too much trouble.
The other statisticians probably already know and use R.
The non-programmer, non-statistician, business types probably aren't interested in your source code--be it Python or R--and will want you to make pretty graphs and give presentations anyways.