Prerequisite: Underscore in Python Show Mangling and how it works In Python, there is something called name mangling, which means that there is limited support for a valid use-case for class-private members basically to avoid name
clashes of names with names defined by subclasses. Any identifier of the form __geek (at least two leading underscores or at most one trailing underscore) is replaced with _classname__geek, where classname is the current class name with a leading underscore(s) stripped. As long as it occurs within the definition of the class, this mangling is done. This is helpful for letting subclasses override methods without breaking intraclass method calls. Python
The mangling rules are designed mostly to avoid accidents but it is still possible to access or modify a variable that is considered private. This can even be useful in special circumstances, such as in the debugger. _Single Leading Underscores So basically one underline at the beginning of a method, function, or data member means you shouldn’t access this method because it’s not part of the API. Let’s look at this snippet of code: Python
The snippet is taken from the Django source code (django/forms/forms.py). This suggests
that errors are property, and it’s also a part of the API, but the method, _get_errors, is “private”, so one shouldn’t access it. __Double Leading Underscores Two underlines, in the beginning, cause a lot of confusion. This is about syntax rather than a convention. double underscore will mangle the attribute names of a class to avoid conflicts of attribute names between classes. For example: Python
__Double leading and Double trailing underscores__ There’s another case of double leading and trailing underscores. We follow this while using special variables or methods (called “magic method”) such as__len__,
__init__. These methods provide special syntactic features to the names. For example, __file__ indicates the location of the Python file, __eq__ is executed when a == b expression is executed. Example: Python
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