That has been addressed in some many other ways by several languages that goes from the C++ way where you actually have namespaces to the C way where you don't worry about it and pick another name. From all of them I find this the most odd way to address it, specially when python was supposed to improve legibility by design (at least for me those underscores are very distracting)
The underscores are distracting on purpose; any method surrounded by double underscores is one that you're virtually never supposed to explicitly call (there's a builtin `next(foo)` in Python 3, for instance)
There's no need to make it not be valid. C++ uses begin() and end() for obtaining iterators to containers, but nothing's stopping you from using those method names for your own purposes.
It's just that if you want to use a few new language niceties like range-based for loops then you'll need to conform to that convention.
In C++ it's fairly common to be calling begin() and end() on containers, where in Python it's not common to call next(), you let the for loop handle it. It's reasonable to rename a function to something ugly when you're never going to be seeing it.
In fact it should never happen, that's what the `iter` and `next` builtins are for. The only use case for calling __next__ by hand is iffy as hell, it's overloading it while inheriting from an iterator.