If people write program logic in python it will run at python speeds. Otherwise you're not really writing python, like nobody says some linux native program is bash because it happens to be launched from a bash script.
But that's how every scripting language obtains good-not-just-decent performance. A strong culture of dropping down to C for any halfway-important library is why PHP's so hard to beat in real-world use, speed-wise (whatever its other shortcomings).
But that's exactly the strength of Python: it's an interface language. It's meant to make pretty sophisticated things like CUDA easy for everyone.