Re: [Qemu-devel] [PATCH v4 1/2] qapi: Open files with encoding='utf-8'

[Eduardo Habkost <ehabkost@redhat.com>]

On Tue, Jun 19, 2018 at 08:28:08AM +0200, Markus Armbruster wrote:
> Eduardo Habkost <ehabkost@redhat.com> writes:
> 
> > On Mon, Jun 18, 2018 at 07:59:57PM +0200, Markus Armbruster wrote:
> >> Python 2 happily reads UTF-8 files in text mode, but Python 3 requires
> >> either UTF-8 locale or an explicit encoding passed to open().  Commit
> >> d4e5ec877ca fixed this by setting the en_US.UTF-8 locale.  Falls apart
> >> when the locale isn't be available.
> >> 
> >> Matthias Maier and Arfrever Frehtes Taifersar Arahesis proposed to use
> >> binary mode instead, with manual conversion from bytes to str.  Works,
> >> but opening with an explicit encoding is simpler, so do that.
> >> 
> >> Since Python 2's open() doesn't support the encoding parameter, we
> >> need to suppress it with a version check.
> >> 
> >> Reported-by: Arfrever Frehtes Taifersar Arahesis <arfrever.fta@gmail.com>
> >> Reported-by: Matthias Maier <tamiko@43-1.org>
> >> Signed-off-by: Markus Armbruster <armbru@redhat.com>
> >> ---
> >>  scripts/qapi/common.py | 17 ++++++++++++++---
> >>  1 file changed, 14 insertions(+), 3 deletions(-)
> >> 
> >> diff --git a/scripts/qapi/common.py b/scripts/qapi/common.py
> >> index 2462fc0291..832f11438a 100644
> >> --- a/scripts/qapi/common.py
> >> +++ b/scripts/qapi/common.py
> >> @@ -16,6 +16,7 @@ import errno
> >>  import os
> >>  import re
> >>  import string
> >> +import sys
> >>  from collections import OrderedDict
> >>  
> >>  builtin_types = {
> >> @@ -340,7 +341,10 @@ class QAPISchemaParser(object):
> >>              return None
> >>  
> >>          try:
> >> -            fobj = open(incl_fname, 'r')
> >> +            if sys.version_info[0] >= 3:
> >> +                fobj = open(incl_fname, 'r', encoding='utf-8')
> >> +            else:
> >> +                fobj = open(incl_fname, 'r')
> >
> > I dislike the Python version check, but getting rid of it would
> > require rewriting the QAPI modules to not use the Python 2 str
> > type (that has different semantics from Python 3 str type).
> 
> The version check is ugly, but it has a property I rather like: when we
> drop support for Python 2, the conditional becomes True, and partial
> evaluation results in the Python 3 code we actually want.
> 
> > The python-future package would help us write code for a single
> > file/string API instead of two different APIs, but it's not a
> > QEMU build dependency (yet?), so this patch is good enough for
> > now.
> 
> Please do not invest more than absolutely necessary in Python 2 support.
> All such investment will turn into technical debt in less than two
> years.  If you must invest, pick a solution that will result in less
> technical debt.  We can accept local ugliness for that.
> 
> In my personal opinion, dumb ideas like supporting Python 2 this close
> to its EOL ought to look ugly.

That's the whole point: python-future allows us to not worry
about Python 2 support in the code anymore because it exposes the
Python 3 string API (and others) even if we're running Python 2.

After we stop supporting Python 2, we can simply delete the "from
__future__ import .*" and "from builtins import .*" lines.

Anyway, I will send a RFC series demonstrating that, and then we
can discuss if it's worth it.  My main worry is not the extra
imports in Python code, but the introduction of a new build
dependency only for a few (one?) releases.


> 
> > Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
> > Acked-by: Eduardo Habkost <ehabkost@redhat.com>
> 
> Uh, what does "Acked-by" add over "Reviewed-by"?

It was supposed to indicate that I agree it can be merged through
other maintainers.  But it looks like this is not part of the
original definition of "Acked-by"?

-- 
Eduardo