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Prolog, for both atoms (predicate names, function names, and constants) and variables [20] Python, for variable names, function names, method names, and module or package (i.e. file) names [3] PHP uses SCREAMING_SNAKE_CASE for class constants; PL/I [21] R, for variable names, function names, and argument names, especially in the tidyverse style ...
In Python, if a name is intended to be "private", it is prefixed by one or two underscores. Private variables are enforced in Python only by convention. Names can also be suffixed with an underscore to prevent conflict with Python keywords. Prefixing with double underscores changes behaviour in classes with regard to name mangling.
In the stdcall and fastcall mangling schemes, the function is encoded as _name@X and @name@X respectively, where X is the number of bytes, in decimal, of the argument(s) in the parameter list (including those passed in registers, for fastcall). In the case of cdecl, the function name is merely prefixed by an underscore.
Python uses names that both start and end with double underscores (so called "dunder methods", as in double underscore) for magic members used for purposes such as operator overloading and reflection, and names starting but not ending with a double underscore to denote private member variables of classes which should be mangled in a manner ...
The frequent use of a double underscores in internal identifiers in Python gave rise to the abbreviation dunder; this was coined by Mark Jackson [3] and independently by Tim Hochberg, [4] within minutes of each other, both in reply to the same question in 2002. [5] [6]
Some languages, notably C, promptly adopted underscores as word separators, and identifiers such as end_of_file are still prevalent in C programs and libraries (as well as in later languages influenced by C, such as Perl and Python). However, some languages and programmers chose to avoid underscores and adopted camel case instead.
For example, in Python, a single leading underscore is a weak private indicator, and affects which identifiers are imported on module import, while a double leading underscore (and no more than one trailing underscore) on a class attribute invokes name mangling. [10]
Python sets are very much like mathematical sets, and support operations like set intersection and union. Python also features a frozenset class for immutable sets, see Collection types. Dictionaries (class dict) are mutable mappings tying keys and corresponding values. Python has special syntax to create dictionaries ({key: value})