I was wondering, is it recommended/Pythonic to define and use custom double underscore variables/functions in a Python script? For example, __tablename__ as used in SQLAlchemy or __validateitem__() (a custom function that validates an item before applying __setitem__() to it).
If it does define that something magic happens, or that that specific variable/function is used indeed in a special way (like the two above examples), I feel it is a good idea using them.
I am interested in arguments on both best coding practices and potential risks in using this kind of naming.
From PEP8:
__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.
So, the advice is not to use the double underscore syntax for your own variables.
来源：https://stackoverflow.com/questions/21587882/how-recommended-is-using-custom-double-underscore-variables-in-python