I use this a lot in my code. If you use an Unix system you should be acquainted with . (current folder) and .. (parent folder), this is basically the same thing but for the modules hierarchy instead of a filesystem hierarchy, and scaling with the number of dots (so ... means parent of parent, and so on). If you do not put any dots it is understood that the module comes from a package in the environment and will check the package outer modules. So you use this notation if your package/module divided into many sub-modules and you need to import things between them, what is not very common.
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