Is generator.next() visible in Python 3?

Question

I have a generator that generates a series, for example:

def triangle_nums():
    '''Generates a series of triangle numbers'''
    tn = 0
    counter = 1
    while True:
        tn += counter
        yield tn
        counter += + 1

In Python 2 I am able to make the following calls:

g = triangle_nums()  # get the generator
g.next()             # get the next value

however in Python 3 if I execute the same two lines of code I get the following error:

AttributeError: 'generator' object has no attribute 'next'

but, the loop iterator syntax does work in Python 3

for n in triangle_nums():
    if not exit_cond:
       do_something()...

I haven't been able to find anything yet that explains this difference in behavior for Python 3.

Answer 1

g.next() has been renamed to g.__next__(). The reason for this is consistency: special methods like __init__() and __del__() all have double underscores (or "dunder" in the current vernacular), and .next() was one of the few exceptions to that rule. This was fixed in Python 3.0. [*]

But instead of calling g.__next__(), use next(g).

[*] There are other special attributes that have gotten this fix; func_name, is now __name__, etc.