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RE: [jasspa] Auto-indentation for Python

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  • Phillips, Steven
    I m kind of in agreement here, by using the indent mode pressing enter will start a new line with the same indent as the previous line then you can either
    Message 1 of 6 , May 20, 2004
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      I'm kind of in agreement here, by using the 'indent' mode pressing enter will start a new line with the same indent as the previous line then you can either press 'tab' to indent more or 'S-tab' (shift-tab) to reduce the indent. Creating an indent rule would suggest that a 'restyle-buffer' should work but this clearly cannot work as the meaning of the program is determined by the indentation and therefore cannot be automatically worked out (otherwise we'd have monkeys writing programs :)

      The one thing that I think could be useful is doing a semi-automatic indentation when the enter key is pressed. In this situation it could do some vaguely useful things, i.e. if the current line ends in a ':' then create a new line with an extra indent, if the current line is blank (just has white spaces) then remove all white spaces on the current line and create a new empty line with no indentation - and I think that is as much as I would dare do considering how important the indentation is. This would best be implemented as a simple macro bound to the return key in python buffers.

      Sakari - How does this sound? If this is okay I will create said macro.

      Steve

      > -----Original Message-----
      > From: first last [mailto:prelude_2_murder@...]
      > Sent: 20 May 2004 09:34
      > To: jasspa@yahoogroups.com
      > Subject: Re: [jasspa] Auto-indentation for Python
      >
      >
      > From what you are saying (and for what I know of Python, I
      > haven't used
      > it for a long, long time) the probable best way to do what you want is
      > to map a key to decrease the indent index (or whatever you call the
      > variable indent uses to keep track of how many levels of indentation
      > has to use for a line).
      >
      > In C-like languages you can have automatic indentation because {} take
      > care of telling ME where to start/end the block, in Python you have to
      > tell the program where you want the indentation, as it is
      > meaningful to
      > the language and it cannot second guess (apart from : starting a
      > block).
      >
      > Correct me if I am wrong but ME just goes to the current indent level
      > when you press enter, so if we have a key (shift + backspace?) that
      > changes the indentation level it should work exactly as expected.
      >
      > Hope this message is helpful...
      >
      > Gabriel
      >
      > --- Sakari Tanhua <stanhua@...> wrote:
      > ---------------------------------
      > Hi Steven,
      >
      > > I would have expected the following to help/work
      > >
      > > indent .hilight.python o "^$" -4
      > >
      > > Which in theory should make a blank line reduce the
      > indentation by 4.
      >
      > I first thought of something like that, too, but the problem is (in
      > addition
      > to the fact that it doesn't work :) ) that it wouldn't allow empty
      > lines in
      > the code between other statements belonging to the same block.
      >
      > > if (type(result) == type('') or type(value) == type('')):
      > > ok = result == value
      > > else:
      > > ok = abs(result - value) <= fuzz
      > > if not ok:
      > > print '!!\t!!\t!! should be', value, 'diff', abs(result -
      > value)
      > >
      > > Is this indented correctly?
      >
      > Yes
      >
      > > If so why is the second 'if' not part of the 'else:'?
      >
      > Python seems a bit weird language at first because the
      > indentation is a
      > critical part of the code. So the second 'if' is not part of
      > the 'else'
      > simply because it's not indented at the 'else' block level!
      >
      > if (type(result) == type('') or type(value) == type('')):
      > ok = result == value
      > else:
      > ok = abs(result - value) <= fuzz
      >
      > if not ok:
      > print '!!\t!!\t!! should be', value, 'diff', abs(result -
      > value)
      >
      > Now it would belong to the else block, so it's now a totally different
      > program, and I only added some whitespace to it. This is Python. :)
      >
      > This is also the root of all evil (well, at least from indent's point
      > of
      > view), as it's impossible for a program to predict how a given line
      > should
      > be indented. But the good thing is that auto indentation for Python is
      > really simple to implement:
      >
      > 1. If the previous line ends with a colon, the second line should be
      > indented one level more.
      >
      > 2. Otherwise, always maintain the previous indentation level,
      > regardless
      > whether or not the previous line contains anything else than
      > whitespaces.
      >
      > 3. The "b" and "c" type indentations (indent(2) terminology) should
      > behave
      > like in C.
      >
      > I guess that'd pretty much do the trick. It should also be noted that
      > the
      > indentation level in Python doesn't necessarily have to be exactly 4
      > spaces.
      > It can be anything, even \t's, but it must be uniform in one
      > block. The
      > style guide favors 4 spaces.
      >
      > After all, maybe it's not wise to try to modify ME's indentation code
      > to
      > support this, but write some macros to change the behavior of
      > backspace
      > and
      > enter?
      >
      > Sakari
      >
      >
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    • Sakari Tanhua
      Steven and Gabriel, ... But why does it lose the indentation level if the previous line contains only whitespaces? I often want to leave empty lines between
      Message 2 of 6 , May 21, 2004
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        Steven and Gabriel,

        > I'm kind of in agreement here, by using the 'indent' mode pressing enter
        > will start a new line with the same indent as the previous line then you
        > can either press 'tab' to indent more or 'S-tab' (shift-tab) to reduce the
        > indent.

        But why does it lose the indentation level if the previous line contains
        only whitespaces? I often want to leave empty lines between statements which
        are at the same indentation level, and after the empty line I certainly
        don't want to hit tab several times to get back to the same indentation
        level.

        I tried to find the code which implements the 'indent' mode but couldn't
        find it. I guess it's written in C but emode.def's MDINDEN was about the
        only thing I could find. Sure I grepped for MDINDEN but didn't find anything
        interesting. Is there already a way to pass parameters to modes to finetune
        their behavior? It'd be nice if the 'indent' mode could be configured to
        maintain the indentation even when the previous line contains only
        whitespaces.

        > Creating an indent rule would suggest that a 'restyle-buffer' should work

        Indeed, so no indent mode for Python then.

        > The one thing that I think could be useful is doing a semi-automatic
        > indentation when the enter key is pressed. In this situation it could do
        > some vaguely useful things, i.e. if the current line ends in a ':' then
        > create a new line with an extra indent,

        Yes, that's good.

        > if the current line is blank (just has white spaces) then remove all white
        > spaces on the current line and create a new empty line with no indentation

        But I don't like this. IMHO it shouldn't remove whitespaces from the current
        line, and it definitely shouldn't lose the indentation on the next line.
        Assuming that's what you meant by "no indentation", i.e. that the next line
        wouldn't contain any whitespaces and the cursor would be at column 0.

        It'd be much better if it would simply retain the indentation level even
        when the previous line contains only whitespaces. That's exactly what GNU
        Emacs does and I never need to hit tab when coding with it, which is nice.
        Furthermore, to reduce the indentation by one level, there's no separate key
        combination for it (like S-tab) but instead I simply hit backspace and it
        eats one indentation level. (Assuming the cursor is right after the
        indentation, of course.)

        I actually wrote a quite primitive auto indentation because I wanted to
        learn the macro language. It's long enough that I don't want to include it
        in this mail, but it can be found here:

        http://www.hut.fi/~stanhua/mypython.emf

        It's probably a bit amateurishly coded because I don't know all the tricks
        of the language. For example, is there a better way to return values from a
        macro than to set #p? variables? If I understood correctly, !return can
        return only boolean values.

        Anyway, it seems to work pretty much the way I like, and though it still
        needs lots of improvements, it's already usable.

        Sakari
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