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For variables, Python has function scope, module scope, and global scope. Names enter context at the start of a scope (function, module, or global scope), and exit context when a non-nested function is called or the scope ends. If a name is used prior to variable initialization, this raises a runtime exception.
Variable scope in Python is implicitly determined by the scope in which one assigns a value to the variable, unless scope is explicitly declared with global or nonlocal. [ 22 ] Note that the closure's binding of a name to some value is not mutable from within the function.
Non-local variables are the primary reason it is difficult to support nested, anonymous, higher-order and thereby first-class functions in a programming language. If the nested function or functions are (mutually) recursive, it becomes hard for the compiler to know exactly where on the call stack the non-local variable was allocated, as the frame pointer only points to the local variable of ...
In computer programming, variable shadowing occurs when a variable declared within a certain scope (decision block, method, or inner class) has the same name as a variable declared in an outer scope. At the level of identifiers (names, rather than variables), this is known as name masking .
Variables and scope: Automatic variables: Each local variable in a function comes into existence only when the function is called, and disappears when the function is exited. Such variables are known as automatic variables. External variables: These are variables that are external to a function and can be accessed by name by any function.
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).
Provide a private naming scope for variables; Identify variables outside the function that are accessible within it; Propagate an exceptional condition out of a function and to handle it in the calling context; Package functions into a container such as module, library, object, or class
Local variables may have a lexical or dynamic scope, though lexical (static) scoping is far more common.In lexical scoping (or lexical scope; also called static scoping or static scope), if a variable name's scope is a certain block, then its scope is the program text of the block definition: within that block's text, the variable name exists, and is bound to the variable's value, but outside ...