::= 语法是什么意思BNF

问题描述

From Simple statement of Python documents, there are expressions like :

expression_stmt ::= starred_expression

解决方案

This is Backus-Naur Form(BNF) notation describing the language.

::= in this context means is defined as .

BNF

From Wikipedia, Backus-Naur form(BNF) in computer science, is a notation technique for context-free grammars, often used to describe the syntax of languages used in computing, such as computer programming languages, document formats, instruction sets and communication protocols.

They are applied wherever desciptions of languages are needed: for instance, in official language specifications, in mannuals, and in textbooks on programming language theory.

References

What does a double colon followed by an equals sign (::=) mean in programming documentation?