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by simias 4537 days ago
My point is that it's not always possible for the editor to know what the indentation is supposed to be because it can't know what the code is supposed to do.

Suppose you have code like this:

    [...]
        if a:
            b
        c
    [...]
And then you paste some snippet you got from somewhere else between b and c:

    [...]
        if a:
            b
    pasted_snippet
        c
    [...]
The editor cannot know how to indent that properly. It's not a problem in most other languages.

Again, I'm not trying to say it's a deal breaker and Python is useless as a result, I just think it's a small mistake in the design of the language. It's like non-breaking switch/case in C, it doesn't make the language unusable but it is an annoyance.
2 comments
pyre 4537 days ago
In that example, a good editor should indent pasted_snippet at least to the first indent level. If you wanted it to be part of the if statement then you could just select the pasted block (both Vim and Emacs should be able to do this with a single command) and indent it by one more.

Python's use of semantic white space is more a function of it's inheritance than anything. It's based off of ABC[1].

[1] http://en.wikipedia.org/wiki/ABC_%28programming_language%29

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Goladus 4537 days ago
The editor cannot know how to indent that properly. It's not a problem in most other languages.

It will have a pretty good idea. If you paste the snippet, then hit 'tab', odds are high that a good editor (I use emacs python-mode) will Do The Right Thing on the first try, although sometimes you'll have to hit tab again or backspace a couple of times to get the right indent level.

Occasionally I need to use a keyboard macro to fix the indent after a paste, but this is very easy to do and doesn't happen to often, really. I'm sure by now with python's popularity there are more advanced indentation management tools but I still just use emacs keyboard macros.

It's a very small price to pay for the huge benefits of semantic whitespace.

Generally the worst case scenario for copy/paste is that I'm using emacs in a terminal window and I forget to switch to fundamental-mode before pasting. Because the terminal is handling the paste, not emacs, python-mode treats it all as if it had been entered one line at a time and auto-indents everything after a colon, then pasting in lines that already have indentation and the result is a complete mess. (but then I just undo it all and re-paste it the right way) GUI emacs doesn't have this problem.

The worst case scenario I can think of for semantic whitespace (outside of copy/paste) is accidentally changing indent level of a piece of code without realizing it and a syntax error doesn't result, meaning there's now a logic flaw in your program you don't know about. Python is more susceptible to that than sort of regression error than most languages. That said, usually that sort of mistake WILL cause a syntax error and be easily fixed.

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