[libvirt] [PATCH] check-symfile: Use pythonesque string formatting instead of perl

[Pavel Hrdina]

On Tue, Nov 26, 2019 at 10:01:11AM +0000, Daniel P. Berrangé wrote:
> On Tue, Nov 26, 2019 at 09:48:31AM +0100, Michal Privoznik wrote:
> > On 11/26/19 9:24 AM, Erik Skultety wrote:
> > > On Mon, Nov 25, 2019 at 05:17:54PM +0100, Michal Privoznik wrote:
> > > > On 11/25/19 4:58 PM, Erik Skultety wrote:
> > > > > On Mon, Nov 25, 2019 at 04:37:36PM +0100, Peter Krempa wrote:
> > > > > > Commit d30a1ad0443 translated the symbol file checker from perl to
> > > > > > python by doing a literal translation in most cases. Unfortunately one
> > > > > > string formatting operation was not really translated into python
> > > > > > leaving users with non-helpful error:
> > > > > > 
> > > > > > 'Symbol $1 is listed twice'
> > > > > > 
> > > > > > Signed-off-by: Peter Krempa <pkrempa at redhat.com>
> > > > > > ---
> > > > > >    scripts/check-symfile.py | 2 +-
> > > > > >    1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > > 
> > > > > > diff --git a/scripts/check-symfile.py b/scripts/check-symfile.py
> > > > > > index 0c02591991..34396b8623 100755
> > > > > > --- a/scripts/check-symfile.py
> > > > > > +++ b/scripts/check-symfile.py
> > > > > > @@ -52,7 +52,7 @@ with open(symfile, "r") as fh:
> > > > > >            line = line.strip(";")
> > > > > > 
> > > > > >            if line in wantsyms:
> > > > > > -            print("Symbol $1 is listed twice", file=sys.stderr)
> > > > > > +            print("Symbol %s is listed twice" % line ,file=sys.stderr)
> > > > > 
> > > > > Not a deal breaker, but IMO should at least the "new" syntax for string
> > > > > formatting using the .format() method (works both with python 2 and 3).
> > > > > 
> > > > > Ideally, we'd move to python 3.6+ (since 2 will die in about 2 months) and
> > > > > started using string interpolation (or f-strings if you want).
> > > > 
> > > > Well, looks like we are not using that anywhere. And frankly, f-strings are
> > > > horrible. This is the most readable style for us, C developers IMO.
> > > 
> > > Can you be more specific on what exactly is horrible about f-strings? IMO it's
> > > actually very intuitive way of formatting strings unlike using the '%'
> > > formatting sign where depending on whether you have 1 or multiple arguments you
> > > may or may not need to use a tuple. F-strings are also a bit faster than the
> > > other formatting methods and because they're evaluated during runtime, you can
> > > evaluate arbitrary expressions, even call functions.
> > 
> > That's exactly what I find horrible. Just consider the following example:
> > 
> >   print(f'a={f(x,n):d}, b={g(x,n):d}')
> > 
> > IMO the following is more readable:
> > 
> >   print("a=%d, b=%d" % (f(x,n), g(x,n)))
> > 
> > Once again, I'm talking about C developers (me specifically). I don't doubt
> > that an experienced python developer finds f-strings a step forward.
> 
> I've plenty of python dev experiance and I still think f-strings  are
> a horrible regression in design.  IMHO it is a good thing to have the
> parameters visually separated from the string, as it makes it clearer
> to read the string being formatted. 

I tend to agree here.  f-strings are not that bad but it allows you to
write ugly code.  It is probably good for interactive python but
otherwise I would prefer the new-style .format() with named arguments:

"Hello {name}".format(name="Pavel")

The major benefit that I see in this style is that it helps translators
to figure out what the substitution will be and the order of arguments
doesn't matter and you can build the dictionary passed to format()
outside of it's call.

Pavel
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