Python interactive mode: calling next without using return value does not advance iterator

Question

If I execute,

a = iter([1,2,3])                                                      
for x in a: 
    print(x) 
    if x==1: 
        z=next(a)

I get

1
3

which I expect, since the call to next advances the iterator and skips the 2.

However in interactive mode (command line), if I remove the z= assignment, and only call next, it behaves very differently.

>>> a = iter([1,2,3])                                                      
>>> for x in a: 
...    print(x) 
...    if x==1: 
...        next(a)

gives me

1
2
3

I'm using Python 3.8.8 in Windows 64 bits. Is this expected? It only happens in interactive mode.

Answer 1

Interpreter echoing back the return value of next() in addition to x being printed each iteration.

>>> a = iter([1,2,3])                                                      
>>> for x in a: 
...    print(x) 
...    if x==1: 
...        next(a)

So 1 and 3 is the output of print(x), 2 the return value from next(). If you assign the output of z=next() things work as expected 1,3 because your z isn't returning or printing. Assigning the result of "next(a)" to a variable inhibits the printing of its' result so that just the alternate values that the "x" loop variable are printed