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

["Daniel P. Berrangé" <berrange@redhat.com>]

On Fri, Mar 01, 2019 at 10:48:04AM -0600, Eric Blake wrote:
> On 3/1/19 10:33 AM, 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 <berrange@redhat.com>
> > ---
> >  configure | 21 ++++++++++++++++++---
> >  1 file changed, 18 insertions(+), 3 deletions(-)
> > 
> > diff --git a/configure b/configure
> > index 540bee19ba..ef2e5bf9f5 100755
> > --- a/configure
> > +++ b/configure
> > @@ -902,7 +902,10 @@ 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
> > +: ${python=${PYTHON-python3 python python2}}
> 
> If I run with PYTHON='/path with spaces/to/mypython',

People who do that are super annoying ;-P

> 
> >  : ${smbd=${SMBD-/usr/sbin/smbd}}
> >  
> >  # Default objcc to clang if available, otherwise use CC
> > @@ -1797,8 +1800,20 @@ EOF
> >  exit 0
> >  fi
> >  
> > -if ! has $python; then
> > -  error_exit "Python not found. Use --python=/path/to/python"
> > +try_python="$python"
> > +python=
> > +for binary in $try_python
> 
> then this ignores my request (trying '/path', 'with', and
> 'spaces/to/mypython', none of which works).
> 
> I think a better approach would be:
> 
> python=
> for binary in "${PYTHON-python3}" python python2

Yeah, that's a nice idea

> 
> > +do
> > +    if has $binary
> 
> if has "$binary"
> 
> > +    then
> > +       python=$binary
> > +       break
> > +    fi
> > +done
> > +
> > +if test -z "$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
> > 
> 
> -- 
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3226
> Virtualization:  qemu.org | libvirt.org

Regards,
Daniel
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