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The terms future, promise, delay, and deferred are often used interchangeably, although some differences in usage between future and promise are treated below. Specifically, when usage is distinguished, a future is a read-only placeholder view of a variable, while a promise is a writable, single assignment container which sets the value of the ...
Python's syntax, though, sometimes leads programmers of other languages to think that closures are not supported. 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]
In Python, auxiliary variables in generator expressions and list comprehensions (in Python 3) have expression scope. In C, variable names in a function prototype have expression scope, known in this context as function protocol scope. As the variable names in the prototype are not referred to (they may be different in the actual definition ...
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 many languages, the scope resolution operator is written ::. In some languages, notably those influenced by Modula-3 (including Python and Go), modules are objects, and scope resolution within modules is a special case of usual object member access, so the usual method operator . is used for scope resolution.
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 .
In formal semantics, the scope of a semantic operator is the semantic object to which it applies. For instance, in the sentence "Paulina doesn't drink beer but she does drink wine," the proposition that Paulina drinks beer occurs within the scope of negation, but the proposition that Paulina drinks wine does not.
However, it is not always idiomatic in such languages, and is specifically discouraged in Python (in favor of context managers and finalizers from the weakref package). [citation needed] However, object lifetimes are not necessarily bound to any scope, and objects may be destroyed non-deterministically or not at all.