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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.
C and C++ are notable in this respect: C99 reserves identifiers that start with two underscores or an underscore followed by an uppercase letter, and further reserves identifiers that start with a single underscore (in the ordinary and tag spaces) for use in file scope; [1] with C++03 further reserves identifiers that contain a double ...
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 Java, the signature of a method or a class contains its name and the types of its method arguments and return value, where applicable. The format of signatures is documented, as the language, compiler, and .class file format were all designed together (and had object-orientation and universal interoperability in mind from the start).
Generally, var, var, or var is how variable names or other non-literal values to be interpreted by the reader are represented. The rest is literal code. The rest is literal code. Guillemets ( « and » ) enclose optional sections.
A variable named with just an underscore often has special meaning. $_ or _ is the previous command or result in many interactive shells, such as those of Python, Ruby, and Perl. In Perl, @_ is a special array variable that holds the arguments to a function. In Clojure, it indicates an argument whose value will be ignored. [11]
In other languages (like Python) this is enforced only by convention (for example, private methods may have names that start with an underscore). In C#, Swift & Kotlin languages, internal keyword permits access only to files present in the same assembly, package, or module as that of the class. [47]
Which character sequences constitute identifiers depends on the lexical grammar of the language. A common rule is alphanumeric sequences, with underscore also allowed (in some languages, _ is not allowed), and with the condition that it can not begin with a numerical digit (to simplify lexing by avoiding confusing with integer literals) – so foo, foo1, foo_bar, _foo are allowed, but 1foo is ...