End/Quitting a function right after it calls another function

a beginner learning python

So, suppose I have 2 functions, A n B

A():  calls B()

B():  usual procedures, #has return values; 

But when a condition is met:`B calls A();# I want function B() to stop/quit and not return anything immediately after calling A() as a new process of A() starts

Is this possible? And safe?Would it be possible through multithreading, which I still haven't learnt