Question

I have a loop where in each iteration I (re)calculate a long vector of values:

try:
    while(1):
        long_vec = recalculate( long_vec )
        last_vec = long_vec.copy()
except KeyboardInterrupt:
    print last_vec

long_vec and last_vec are numpy arrays.

My question is: can I be sure that when I press CTRL+C , it won’t break copy() function, and last_vec is not broken?

Answer 1

It’s not the .copy() that matters, it’s the subsequent assignment of the reference (last_vec =) that does.

I believe the assignment is atomic in CPython (i.e. it requires a single bytecode instruction).

In other words, last_vec can either contain the value from the previous iteration, or the copied value from the current iteration. Pressing Ctrl-C cannot result in last_vec containing a partial copy of the new value.