I came across the sentence,

In Python, indentation is semantically meaningful.

I'm not sure I understand what "semantically meaningful" means here.

Also, since indentations are used to delimit the if and else blocks of coniditional expressions in Python, wouldn't they be considered to be part of the language grammar and therefore "syntactically meaningful"? (I cannot find mention of them in the docs for conditional expressions.)

CodePudding user response：

This question is mostly useful for pedantry, since the answer won't change the way you write your code.

However, I would say: in Python, spaces are syntactically meaningful, and indentation is semantically meaningful.

The number of spaces at the start of a logical line (in the sense as defined in the documentation) defines the indentation level for that line, by comparing the number of spaces to the same number for the previous logical line. It either matches the previous number (continue current block), is greater (increase level and start new block) or matches a previous number of spaces (decrease level, end current block, continue matched block). If it doesn't match a previous level, that's an indentation error. That's the syntactic meaning of spaces.

Once Python knows the indentation level, that decides the meaning of the line (i.e. continue a block, start a new one, or continue a previous block and ending the current) - these are the semantics of the indentation level.

In other words: spaces are syntax, indentation is semantics.

CodePudding user response：

I think they should have said "semantically meaningful", but the distinction is somewhat fuzzy. TechDifferences says:

The syntax of a programming language is a collection of rules to specify the structure or form of code whereas semantics refers to the interpretation of the code or the associated meaning of the symbols, characters or any part of a program.

Since indentation determines things like whether a line is part of a function or loop, and that impacts things like variable scope, it could be considered to affect the "associated meaning" of the symbols.