[Python-ideas] with statement syntax forces ugly line breaks?

[Michael Foord]

On 9 September 2010 14:53, M.-A. Lemburg <mal at egenix.com> wrote:

> Michael Foord wrote:
> > On 9 September 2010 14:32, M.-A. Lemburg <mal at egenix.com> wrote:
> >
> >> [snip...]
> >> Why do you need to put everything on one line ?
> >>
> >> afh = open(args.actual, encoding="utf-8")
> >> efh = open(args.expected, encoding="utf-8")
> >>
> >> with afh, efh:
> >>   ...
> >>
> >> In the context of files, the only purpose of the with statement
> >> is to close them when leaving the block.
> >>
> >>>>> a = open('/etc/passwd')
> >>>>> b = open('/etc/group')
> >>
> >
> > If my understanding is correct (which is perhaps unlikely...), using a
> > single line will close a if opening b fails. Whereas doing them
> separately
> > before the with statement risks leaving the first un-exited if creating
> the
> > second fails.
>
> Right, but if you stuff everything on a single line, your
> error handling will have a hard time figuring out which of
> the two failed to open.
>

If you *need* to distinguish at a higher level then you have no choice. I
was really just pointing out that there are *semantic* differences as well,
and in fact the code you posted is less safe than the one line version. You
lose some of the error handling built-in to context manager creation.

Michael


>
> I was under the impression that Mark wanted to "protect" the
> inner block of the with statement, not the context manager
> creation itself.
>
> As usual: hiding away too much stuff in your closet makes things
> look tidy, but causes a hell of a mess if you ever need to open
> it again :-)
>
> > Michael
> >
> >
> >>>>> with a,b: print a.readline(), b.readline()
> >> ...
> >> at:x:25:25:Batch jobs daemon:/var/spool/atjobs:/bin/bash
> >> at:!:25:
> >>
> >>>>> a
> >> <closed file '/etc/passwd', mode 'r' at 0x7f0093e62390>
> >>>>> b
> >> <closed file '/etc/group', mode 'r' at 0x7f0093e62420>
> >>
> >> --
> >> Marc-Andre Lemburg
> >> eGenix.com
> >>
> >> Professional Python Services directly from the Source  (#1, Sep 09 2010)
> >>>>> Python/Zope Consulting and Support ...        http://www.egenix.com/
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> >>>>> mxODBC, mxDateTime, mxTextTools ...        http://python.egenix.com/
> >> ________________________________________________________________________
> >> 2010-08-19: Released mxODBC 3.1.0
> http://python.egenix.com/
> >> 2010-09-15 <http://python.egenix.com/%0A2010-09-15>: DZUG Tagung,
> Dresden,
> >> Germany                   6 days to go
> >>
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> >>
> >>
> >>   eGenix.com Software, Skills and Services GmbH  Pastor-Loeh-Str.48
> >>    D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg
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> >>
> >
> >
> >
>
> --
> Marc-Andre Lemburg
> eGenix.com
>
> Professional Python Services directly from the Source  (#1, Sep 09 2010)
> >>> Python/Zope Consulting and Support ...        http://www.egenix.com/
> >>> mxODBC.Zope.Database.Adapter ...             http://zope.egenix.com/
> >>> mxODBC, mxDateTime, mxTextTools ...        http://python.egenix.com/
> ________________________________________________________________________
> 2010-08-19: Released mxODBC 3.1.0              http://python.egenix.com/
> 2010-09-15 <http://python.egenix.com/%0A2010-09-15>: DZUG Tagung, Dresden,
> Germany                   6 days to go
>
> ::: Try our new mxODBC.Connect Python Database Interface for free ! ::::
>
>
>   eGenix.com Software, Skills and Services GmbH  Pastor-Loeh-Str.48
>    D-40764 Langenfeld, Germany. CEO Dipl.-Math. Marc-Andre Lemburg
>           Registered at Amtsgericht Duesseldorf: HRB 46611
>               http://www.egenix.com/company/contact/
> _______________________________________________
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