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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Mon, 25 May 2015 22:34:51 -0600
Subject: Re: Documentaion of dunder methods
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Xref: csiph.com comp.lang.python:91227

On Mon, May 25, 2015 at 8:17 PM, Steven D'Aprano <steve@pearwood.info> wrote:
> PEP 8 states that developers should never invent their own dunder methods:
>
>     __double_leading_and_trailing_underscore__ :
>         "magic" objects or attributes that live in user-controlled
>         namespaces. E.g. __init__ , __import__ or __file__ . Never
>         invent such names; only use them as documented.
>
> https://www.python.org/dev/peps/pep-0008/#naming-conventions
>
>
> In other words, dunder methods are reserved for use by the core developers
> for the use of the Python interpreter.
>
> Apart from PEP 8, is this documented anywhere in the official documentation?
> If so, I have been unable to find it.

https://docs.python.org/3/reference/lexical_analysis.html#reserved-classes-of-identifiers