build: depend on python2 specifically

[rpodgorny]

This solves the problem of not being able to build node on system
where both python2 and python3 is installed and python3 is the
default.

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• commit message follows commit guidelines

Affected core subsystem(s)

build system

...i will send patches for "dep" and "tools" to their respective upstream but this solves the problem for the node part.

[mscdex]

Hrmm... I'm curious if there are any modern platforms/distributions that only provide python and not python2 (e.g. perhaps python for 2.x and python3 for 3.x). Windows is probably one of the more obvious potential platforms that could be included in that list.

[rpodgorny]

none that i'm aware of (but i'm no expert)... but, imho, at least on linux, the good practice is to have python2 and/or python3 and python being just symlink to one of those...

[jbergstroem]

I think this have been brought up previously. There are too many ways python(2) is installed; I think we shouldn't rock the boat on this one. @bnoordhuis thoughts?

[Fishrock123]

I do not have python2. OS X 10.10.5.

[vsemozhetbyt]

FWIW:

c:\>python2
'python2' is not recognized as an internal or external command, operable program or batch file.

I have only Python 2.7.13 on Windows 7 x64. Would python2 appear if I install Python 3x?

[bnoordhuis]

I do not have python2. OS X 10.10.5.

Yes, this is the clincher. OS X systems don't have a python2 binary.

[gibfahn]

Yes, this is the clincher. OS X systems don't have a python2 binary.

Given the above, I think that #11375 is a better solution to this problem.

[rpodgorny]

hmm, just found this. ...adding for reference: #9512
i'm afraid this will only keep coming as more and more systems default to python3.

[BridgeAR]

As #11375 has landed and this is not going to fully work I am going to close this. If you feel that it should be reopened, please do so.