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

[Eduardo Habkost]

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.


> +do
> +    if has "$binary"
> +    then
> +     python="$binary"
> +     break

Tabs/spaces mix up here.  (I thought Patchew/checkpatch.pl would
detect this?)

> +    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