configure fails on linux for distributions using python 3 as default

[shannon-nii]

• Version: V7.0.0
• Platform: Linux manjaro-vm 4.8.5-2-MANJARO deps: update openssl to 1.0.1j #1 SMP PREEMPT Sun Oct 30 11:26:24 UTC 2016 x86_64 GNU/Linux
• Subsystem:

Currently the configure script executes via "python", this works perfectly fine on systems that use python 2.x as their default python but it fails on systems that use python 3.x. Would it be possible/feasible to adjust it to execute via "python2" instead of "python"? Alternatively an updated configure script that works on 2.x and 3.x python would be good.

Python 3 error when trying to run configure:

Is there possibly just a missing module for python3?

[silverwind]

This also applies to Arch Linux on which python is actually python3. I think it'd be great if we could apply __future__ and friends to support both versions.

[bnoordhuis]

That won't help. configure does import gyp and gyp does not pretend to be python3-compatible. Changing the shebang to python2 breaks systems with no python2 binary. I think that includes OS X.

[silverwind]

Indeed, macOS has no python2, only python2.6 and python2.7. The version from homebrew does feature all the symlinks including python2, but I'm not sure we can require that.

As for gyp: There's https://bugs.chromium.org/p/gyp/issues/detail?id=36, but it's unlikely gyp will ever gain support for Python3 as it's pretty much a dead project from what I understand.

[jbergstroem]

There's a bunch of issues in the node-gyp repo that are similar to this. Unfortunately, the conclusion that @silverwind mentioned is likely what we can expect; upstream gyp won't get ported to python 3.

[shannon-nii]

manjaro is based on arch linux and it has python2 and python2.7 links
This should be the same for arch linux but i'm not sure about other linux distributions.
For now I run the configure script directly via python 2.x.
Would it be possible to at least add a check for the python version and show an error message if python3 is detected with an advise to run the script via python2?

[bnoordhuis]

I don't think so. The python interpreter will throw syntax errors before the script even gets a chance to run.

The only way to work around that is to split off the main configure script into a separate script and leave only a loader stub that is legal python 2 + 3 but that seems like overcomplicating things when the python 2 prerequisite is listed in BUILDING.md.

[silverwind]

I think it should be possible to make the file parseable in Python 3 and print a error when python >= 3. This should work as long as Python does not evaluate import before execution.

For the except issue in the original post, we can apply this workaround.

[kalrover]

Can you guys help me check my first PR on node. If there is any problems, let me know.

[zenhack]

A couple ideas:

1. We demand specifically python 2.7, and then do #!/usr/bin/env python2.7, or
2. We put some logic like this at the top of the script:

#!/usr/bin/env sh

# Find a python 2 executable:
python_executable="`which python2"
if [ -z "$python_executable" ]; then
  python_executable="`which python2.7`"
fi
if [ -z "$python_executable" ]; then
  python_executable="`which python2.6`"
fi
if [ -z "$python_executable" ]; then
  printf 'Error: could not find python 2 executable\n' >&2
  exit 1
fi

# Copy the remainder of this script (which is python) to a new file and execute it with
# python instead of sh:
tmpfile="`mktemp`"
cat "$0" | tail -n +22 > "$tmpfile"
chmod +x "$tmpfile"
exec "$python_executable" "tmpfile" $@

(1) is certainly simpler.

[zenhack]

Αnother option is to special-case MacOS, doing something like:

case `uname` in
  darwin) python_executable="`which python2.7`" ;; # Or whatever uname returns on OS X; I don't have a live system handy.
  *) python_executable="`which python`";;
esac

[silverwind]

This is fixed by #9657.

@zenhack generally good ideas, but I think the current solution is good enough as the user will know what to do from the error message. Spawning another python child process doesn't seem like the cleanest solution to me.