Re: [Qemu-devel] [PATCH v2] configure: automatically pick python3 is available

[Daniel P . Berrangé]

On Wed, Mar 27, 2019 at 01:38:07PM -0300, Eduardo Habkost wrote:
> On Tue, Mar 19, 2019 at 11:02:08AM +0000, Daniel P. Berrangé wrote:
> > Unless overridden via an env var or configure arg, QEMU will only look
> > for the 'python' binary in $PATH. This is unhelpful on distros which
> > are only shipping Python 3.x (eg Fedora) in their default install as,
> > if they comply with PEP 394, the bare 'python' binary won't exist.
> > 
> > This changes configure so that by default it will search for all three
> > common python binaries, preferring to find Python 3.x versions.
> > 
> > Signed-off-by: Daniel P. Berrangé <address@hidden>
> > ---
> > 
> > Changed in v2:
> > 
> >  - Rewrote to follow Eric's suggested approach
> > 
> >  configure | 18 +++++++++++++++---
> >  1 file changed, 15 insertions(+), 3 deletions(-)
> > 
> > diff --git a/configure b/configure
> > index 7071f52584..028453a5a6 100755
> > --- a/configure
> > +++ b/configure
> > @@ -901,7 +901,18 @@ fi
> >  
> >  : ${make=${MAKE-make}}
> >  : ${install=${INSTALL-install}}
> > -: ${python=${PYTHON-python}}
> > +# We prefer python 3.x. A bare 'python' is traditionally
> > +# python 2.x, but some distros have it as python 3.x, so
> > +# we check that before python2
> > +python=
> > +for binary in "${PYTHON-python3}" python python2
> 
> I wouldn't like configure to try any other python binary if one
> was explicitly specified using "--python=".  It might make
> packaging mistakes go completely undetected.

This code runs long before --python arg is parsed. It is just
setting up the default value for the $python  env in configure.

Later code will replace this default if --python is given, so
we still honour --python to same extent as before this patch.

> 
> 
> > +do
> > +    if has "$binary"
> > +    then
> > +   python="$binary"
> > +   break
> 
> Tabs/spaces mix up here.  (I thought Patchew/checkpatch.pl would
> detect this?)

Opps. Perhaps not for the configire script.

> 
> > +    fi
> > +done
> >  : ${smbd=${SMBD-/usr/sbin/smbd}}
> >  
> >  # Default objcc to clang if available, otherwise use CC
> > @@ -1797,8 +1808,9 @@ EOF
> >  exit 0
> >  fi
> >  
> > -if ! has $python; then
> > -  error_exit "Python not found. Use --python=/path/to/python"
> > +if test -z "$python"
> > +then
> > +    error_exit "Python not found. Use --python=/path/to/python"
> >  fi
> >  
> >  # Note that if the Python conditional here evaluates True we will exit
> > -- 
> > 2.20.1
> > 
> > 
> 
> -- 
> Eduardo

Regards,
Daniel
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