How big is the speed difference between C# and Python ?

Question

I am a biginner, I was advised to start learning Python because I'm planning to build prototypes programs in a scientific environement. Until now, Python seems very fun to me. But I read everywhere that the bad side about using Python is the speed of execution. I know I may build some complex data-using program (when I'll be skilled enough). Well, the question then is in my title. If any of you has some experience bin that field ... thank you !

Answer 1

You can change .py to .exe with py2exe etc.

Answer 2

A lot.
C++ and C# apparently does 9*10^2 times more calculations than Python in one second.
Says my CS teacher. (computer studies BTW)

Answer 3

Python is slowest.
Python is literally, turtle.
(import 🐢)