Yes they do take it into consideration but there is no way for you to know how they consider it.
I know it's not the answer you wanted, but it's the truth. The only peace of mind I can offer is that people don't like seeing other people fail. So I strongly doubt this is a game of Russian roulette. Either language should be equally received.
You said Python is "easier" but you could have also said one of these many subjective comparisons.
- a dynamic language versus a typed language
- a slow language versus a fast language
- an easy to debug language versus to a difficult one
- an open source language versus an ANSI standard?
You're comparing apples and oranges here.
Knowing which language they consider the right pick is as subjective as asking if Python is better than C++. The answer depends on who you're asking.
It's your personal choice, and they want you to pick one. The key here is that it's an opportunity to tell them which you'd prefer to work with when you first start at your new job. So it's about picking one you can successfully complete the challenge with, but also picking one that you'll be happy using.
So pick the language that will bring you the most fulfillment and also complete the challenge.
You might pick the wrong one, or maybe there is no wrong one. The point here is to be true to yourself about which you'd prefer. That's all you have control over.