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From: Devin Jeanpierre <jeanpierreda@gmail.com>
Date: Fri, 23 Dec 2011 02:21:01 -0500
Subject: Re: Idiom for shelling out to $EDITOR/$PAGER?
To: Cameron Simpson <cs@zip.com.au>
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> Anyway, look it up; it has an autodelete mode etc.

The autodelete isn't useful in this context. The file needs to be
closed and then reopened again; with the autodelete option, the
closing would delete the file, preventing it from being opened by the
text editor or reopened to check contents.

(As far as I know, the race condition inherent in this is unavoidable.
At least on windows, but I couldn't figure out any other way on Linux
either.)

-- Devin

On Fri, Dec 23, 2011 at 1:02 AM, Cameron Simpson <cs@zip.com.au> wrote:
> On 22Dec2011 22:16, Tim Chase <python.list@tim.thechases.com> wrote:
> | After a little searching, I've not been able to come up with what
> | I'd consider canonical examples of consider calling an external
> | editor/pager on a file and reading the results back in. =C2=A0(most of =
my
> | results are swamped by people asking about editors written in
> | Python, or what the best editors for Python code are)
> |
> | The pseudocode would be something like
> |
> | =C2=A0 def edit_text(data):
> | =C2=A0 =C2=A0 temp_fname =3D generate_temp_name()
> | =C2=A0 =C2=A0 try:
> | =C2=A0 =C2=A0 =C2=A0 f =3D file(temp_fname, 'w')
> | =C2=A0 =C2=A0 =C2=A0 f.write(data)
> | =C2=A0 =C2=A0 =C2=A0 f.close()
> | =C2=A0 =C2=A0 =C2=A0 before =3D info(temp_fname) # maybe stat+checksum?
> | =C2=A0 =C2=A0 =C2=A0 editor =3D find_sensible_editor()
> | =C2=A0 =C2=A0 =C2=A0 subprocess.call([editor, temp_fname])
> | =C2=A0 =C2=A0 =C2=A0 if before =3D=3D info(temp_fname):
> | =C2=A0 =C2=A0 =C2=A0 =C2=A0 return None
> | =C2=A0 =C2=A0 =C2=A0 else:
> | =C2=A0 =C2=A0 =C2=A0 =C2=A0 return file(temp_fname).read()
> | =C2=A0 =C2=A0 finally:
> | =C2=A0 =C2=A0 =C2=A0 delete_if_exists(temp_fname)
> |
> | However there are things to watch out for in this lousy code:
> |
> | -race conditions, unique naming, and permissions on the temp file
>
> NamedTemporaryFile is your friend.
>
> | -proper & efficient detection of file-change, to know whether the
> | user actually did anything
>
> Wait for the editor to exit?
> In that scenario I go for:
> =C2=A0- wait for edit to exit
> =C2=A0- if exit status 0 and file non-empty, trust it
> =C2=A0 =C2=A0(subject to parse issues afterwards of course)
>
> | -cross-platform determination of a sensible editor (that blocks
> | rather than spawns), using platform conventions like
> | os.environ['EDITOR']
>
> os.environment.get('EDITOR', 'vi')?
>
> Some platforms have an executable called "editor" that solves that
> problem (absent $EDITOR); MacOSX has "open", though it won't be running
> a blocking editor, alas.
>
> You may need some knowledge of the local system. On a terminal? Easy,
> use $EDITOR. No terminal, but $DISPLAY? xterm -e "$EDITOR temp_file",
> or the like. No terminal, no $DISPLAY, macosx? I have an incantation
> somewhere...
>
> | -cleanup deletion of the temp-file
>
> NamedTemporaryFile is your friend.
>
> | I presume the code for spawning $PAGER on some content would look
> | pretty similar.
>
> Yep.
>
> | Any good example code (or blog posts, or other links) that has been
> | battle-tested?
>
> Hmm. Nothing directly to had, but regarding the temp file:
>
> =C2=A0# write contents of the file `fp` into a temp file
> =C2=A0with NamedTemporaryFile('w', dir=3Dos.path.join(self.dir, 'tmp')) a=
s T:
> =C2=A0 =C2=A0T.write(fp.read())
> =C2=A0... do stuff with T.name (the temp file name).
>
> Anyway, look it up; it has an autodelete mode etc.
>
> Cheers,
> --
> Cameron Simpson <cs@zip.com.au> DoD#743
> http://www.cskk.ezoshosting.com/cs/
>
> I have always been a welly man myself. They are superb in wet grass, let
> alone lagoons of pig shit. =C2=A0 =C2=A0 =C2=A0- Julian Macassey
> --
> http://mail.python.org/mailman/listinfo/python-list