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In computer programming, a nested function (or nested procedure or subroutine) is a named function that is defined within another, enclosing, block and is lexically scoped within the enclosing block – meaning it is only callable by name within the body of the enclosing block and can use identifiers declared in outer blocks, including outer ...
The term closure is often used as a synonym for anonymous function, though strictly, an anonymous function is a function literal without a name, while a closure is an instance of a function, a value, whose non-local variables have been bound either to values or to storage locations (depending on the language; see the lexical environment section below).
In computer programming, scope is an enclosing context where values and expressions are associated. The scope resolution operator helps to identify and specify the context to which an identifier refers, particularly by specifying a namespace or class. The specific uses vary across different programming languages with the notions of scoping.
Immediately invoked function expressions may be written in a number of different ways. [3] A common convention is to enclose the function expression – and optionally its invocation operator – with the grouping operator, [4] in parentheses, to tell the parser explicitly to expect an expression.
A fundamental distinction in scope is what "part of a program" means. In languages with lexical scope (also called static scope), name resolution depends on the location in the source code and the lexical context (also called static context), which is defined by where the named variable or function is defined.
Python has nested scope, but not the ability to modify variables in outer lexical scopes (except for globals, and via reflexion). Therefore, Python doesn't have closures. It's that simple. --Lament. Admittedly Python closures are broken in this respect compared to Scheme, but this is overstated.
Enclosing subroutine context Some programming languages (e.g., Pascal and Ada) support declaration of nested subroutines, which are allowed to access the context of their enclosing routines, i.e., the parameters and local variables within the scope of the outer routines. Such static nesting can repeat (a function declared within a function ...
Such structure limits references to the class name to within the scope where the class is declared. Depending on the semantic rules of the language, there may be additional restrictions on local classes compared to non-local ones. One common restriction is to disallow local class methods to access local variables of the enclosing function.