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

[Michal Privoznik]

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.

Michal