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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})
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 ...
Python has data classes which provides equality testing and can be made immutable using the frozen parameter. [21] It overrides the __str__ dunder method. [22] This example implementation includes a static method which can be used to initialize a new instance with a randomly generated universally unique identifier (UUID).
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.
Terminal symbols are the concrete characters or strings of characters (for example keywords such as define, if, let, or void) from which syntactically valid programs are constructed. Syntax can be divided into context-free syntax and context-sensitive syntax. [7] Context-free syntax are rules directed by the metalanguage of the programming ...
Fortran and PL/I identify keywords by context, while Algol 60 and Algol 68 generally use stropping to distinguish keywords from programmer-defined identifiers, e.g. .if or 'if or 'if'is a keyword distinct from identifier if. Most programming languages have a standard library (or libraries), e.g. mathematical functions sin, cos, etc.
Examples of common tokens Token name (Lexical category) Explanation Sample token values identifier: Names assigned by the programmer. x, color, UP: keyword: Reserved words of the language. if, while, return: separator/punctuator: Punctuation characters and paired delimiters.}, (, ; operator: Symbols that operate on arguments and produce results ...
Python 3.0, released in 2008, was a major revision not completely backward-compatible with earlier versions. Python 2.7.18, released in 2020, was the last release of Python 2. [37] Python consistently ranks as one of the most popular programming languages, and has gained widespread use in the machine learning community. [38] [39] [40] [41]