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

[Daniel P. Berrangé]

On Tue, Nov 26, 2019 at 11:25:28AM +0100, Pavel Hrdina wrote:
> 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.

Note those advantages are already possible with traditional syntax

  "Hello %(name)s" % { name: "Pavel"}

but for our build scripts this is academic as we're never going to
do translation of anything in them.

Regards,
Daniel
-- 
|: https://berrange.com      -o-    https://www.flickr.com/photos/dberrange :|
|: https://libvirt.org         -o-            https://fstop138.berrange.com :|
|: https://entangle-photo.org    -o-    https://www.instagram.com/dberrange :|