Python: Why isn't "next()" called "__next__()"

Question

I'm using Python 2.7.

By convention, builtin methods like __iter__, __init__, __str__, etc. have the double underscore to identify them as such. Why doesn't the next() function have this?

It features alongside the other built-in functions here: https://docs.python.org/2/library/functions.html and this doesn't seem like a very consistent convention.

Answer 1

The built-in function doesn't have __ because none of the built-ins do. You're confusing built-ins (like str) with special methods (like __str__).

Now the special method called by the built-in next is also called next in Python 2.7, but that naming was recognized as an accident and changed to __next__ in Python 3.

Answer 2

It was in Python v3.x. And is still there for backwards compatibility. From http://docs.pythonsprints.com/python3_porting/py-porting.html:

Python 3 introduced a next() function to replace the next() method on iterator objects. Rather than calling the method on the iterator, the next() function is called with the iterable object as its sole parameter, which calls the underlying __next__() method.