What is the goal here?
If you are looking for outsourcing, you usually look for shops that are able to deliver high quality results. So is the language really important?
If you have 3 shops that delivers the same level of quality at the same cost on 3 different languages then choosing the language may be the next thing.
In my experience finding ONE shop that deliver great results without braking the bank is already a big challenge.
Unless you have a local team that is an expert in Python that can take over why do you want a Python shop?
And even if you have a local team, would not be better, to have them develop the product since the beginning that going later through the pain of the transition?
I am not advocating that Pyhon is not the best option, just that you may not want to focus on the language in your search.