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The following is an example of indentation blocks in Python; a popular off-side rule language. In Python, the rule is taken to define the boundaries of statements rather than declarations. In Python, the rule is taken to define the boundaries of statements rather than declarations.
In computer programming, indentation style is a convention, a.k.a. style, governing the indentation of blocks of source code.An indentation style generally involves consistent width of whitespace (indentation size) before each line of a block, so that the lines of code appear to be related, and dictates whether to use space or tab characters for the indentation whitespace.
Python borrows this feature from its predecessor ABC: instead of punctuation or keywords, it uses indentation to indicate the run of a block. In so-called "free-format" languages—that use the block structure derived from ALGOL —blocks of code are set off with braces ( { } ) or keywords.
Python uses whitespace indentation, rather than curly brackets or keywords, to delimit blocks. An increase in indentation comes after certain statements; a decrease in indentation signifies the end of the current block. [94] Thus, the program's visual structure accurately represents its semantic structure. [95]
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.
Many computer languages use block indentation to demarcate blocks of source code. Indentation is essentially the same regardless of whether the writing system is left-to-right (e.g. Latin and Cyrillic) or right-to-left (e.g. Hebrew and Arabic) when considering line beginning and end. For example, indenting at the beginning of line means on the ...
The off-side rule (blocks determined by indenting) can be implemented in the lexer, as in Python, where increasing the indenting results in the lexer emitting an INDENT token and decreasing the indenting results in the lexer emitting one or more DEDENT tokens. [10]
Python relies on the off-side rule, using indenting to indicate and implement control structure, thus eliminating the need for bracketing (i.e., {and }). However, copying and pasting indented code can cause problems, because the indent level of the pasted code may not be the same as the indent level of the target line.