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If a block is used to set the value of a variable, block scope requires that the variable be declared outside of the block. This complicates the use of conditional statements with single assignment. For example, in Python, which does not use block scope, one may initialize a variable as such:
Pointers to block and block literals are marked with ^. Normal local variables are captured by value when the block is created, and are read-only inside the block. Variables to be captured by reference are marked with __block. Blocks that need to persist outside of the scope they are created in may need to be copied. [20] [21]
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})
A block is a grouping of code that is treated collectively. Many block syntaxes can consist of any number of items (statements, expressions or other units of code) – including one or zero. Languages delimit a block in a variety of ways – some via marking text and others by relative formatting such as levels of indentation.
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 computer programming, a block or code block or block of code is a lexical structure of source code which is grouped together. Blocks consist of one or more declarations and statements . A programming language that permits the creation of blocks, including blocks nested within other blocks, is called a block-structured programming language .
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 ...
Upon leaving the using-block, the compiler guarantees that the stm object is released, effectively binding the variable to the file stream while abstracting from the side effects of initializing and releasing the file. Python's with statement and Ruby's block argument to File.open are used to similar effect.