The planned Python probe is "python --version". Note that currently, "vpython" will already call "python --version" on its target executable in order to determine whether or not it is the desired Python version. The plan is to have the "vpython" probe implementation forward the output from its "--version" probe call so that no additional "exec" is necessary.

The following revision refers to this bug:
  https://chromium.googlesource.com/external/github.com/luci/luci-go.git/+/85885811d2157568a42bb39001ab39345724555c

commit 85885811d2157568a42bb39001ab39345724555c
Author: dnj <dnj@google.com>
Date: Wed Jun 07 17:15:47 2017

Update Probe to be a general-purpose library.

Copy "probe" from "infra":
https://chromium.googlesource.com/infra/infra/+/444e6a3f1c2cac2a8b1232aa1321c2f4cc1ae2b0/go/src/infra/tools/git

Generalize it so that it can be used by other wrappers (notably
"vpython").

BUG= chromium:730649 
TEST=unit

Review-Url: https://codereview.chromium.org/2932443002

[add] https://crrev.com/85885811d2157568a42bb39001ab39345724555c/common/system/prober/probe.go
[add] https://crrev.com/85885811d2157568a42bb39001ab39345724555c/common/system/prober/probe_test.go
[add] https://crrev.com/85885811d2157568a42bb39001ab39345724555c/common/system/prober/probe_unix.go
[add] https://crrev.com/85885811d2157568a42bb39001ab39345724555c/common/system/prober/probe_windows.go

The following revision refers to this bug:
  https://chromium.googlesource.com/external/github.com/luci/luci-go.git/+/5cf5e3db67fbf52c83ae0875d70d58ece1b73b86

commit 5cf5e3db67fbf52c83ae0875d70d58ece1b73b86
Author: dnj <dnj@google.com>
Date: Wed Jun 07 18:15:12 2017

[vpython] Implement smart probing.

Use the "prober" package to enable "vpython" to probe for its
wrapped Python instance without risk of hitting another "vpython"
instance. Previously, identification was just done by name.

This allows "vpython" to be named "python" without infinitely calling
itself.

BUG= chromium:730649 
TEST=local

Review-Url: https://codereview.chromium.org/2925723004

[modify] https://crrev.com/5cf5e3db67fbf52c83ae0875d70d58ece1b73b86/vpython/application/application.go
[add] https://crrev.com/5cf5e3db67fbf52c83ae0875d70d58ece1b73b86/vpython/application/probe.go
[modify] https://crrev.com/5cf5e3db67fbf52c83ae0875d70d58ece1b73b86/vpython/python/find.go
[modify] https://crrev.com/5cf5e3db67fbf52c83ae0875d70d58ece1b73b86/vpython/python/interpreter.go
[modify] https://crrev.com/5cf5e3db67fbf52c83ae0875d70d58ece1b73b86/vpython/venv/config.go
[modify] https://crrev.com/5cf5e3db67fbf52c83ae0875d70d58ece1b73b86/vpython/venv/venv_test.go

why vpython would be named "python" or "python2.7"?

Chat w/ iannucci@, possibly actually using it as a Python entry point w/ a default VirtualEnv environment exported by BuildBot / LUCI via environment variable.