If what you said were true, wouldn't it make a lot more sense for OP to be making a joke about how even if the source includes multi threading, all his extra cores are wasted? And make your original comment suggesting a coding issue instead of a language issue pretty misleading?
But what you said is not correct. I just did a dumb little test
import threading
import time
def task(name):
time.sleep(600)
t1 = threading.Thread(target=task, args=("1",))
t2 = threading.Thread(target=task, args=("2",))
t3 = threading.Thread(target=task, args=("3",))
t1.start()
t2.start()
t3.start()
And then ps -efT | grep python and sure enough that python process has 4 threads. If you want to be even more certain of it you can strace -e clone,clone3 python ./threadtest.py and see that it is making clone3 syscalls.