This option simplifies the configuration options:
1) `g:python{,3}_host_prog` is not set.
Neovim tries its best to find a suitable interpreter. This means calling
exepath(), potentially multiple times, and a system('python -c ...') with
the first found interpreter, to get the Python version.
2) `g:python{,3}_host_prog` is set.
Avoids everything of the above. No safety checks, no training wheels. Fast
host startup time!
This also checks the major/min version only for expected return codes.
With pyenv, you might get the following (return code 127):
pyenv: python3.4: command not found
The `python3.4' command exists in these Python versions:
3.4.3
3.4.3/envs/tmp-3.4.3-eElS6Y
tmp-3.4.3-eElS6Y
"python -c" returns 1 in case of an error. Use a return code of 2 if
the Neovim module is not found to distinguish these cases.
Verify the interpreter version before checking for an installed Neovim
module. Show a new error message if the Python interpreter version
is below the minimum required version.
Always use "pkgutil" to determine if the Neovim module is installed.
In contrast to "importlib", which was used for Python 3,
"pkgutil.find_loader" is available for all Python versions [1,2].
"pkgutil.find_loader" internally uses "importlib" for Python >= 3.3 [2].
Also, the previously used "importlib.find_loader" is only available
since Python 3.3 (so checking the major Python version was not enough)
and deprecated since Python 3.4 [3].
Finally, conditioning on the major version in Vimscript was incorrect,
as checking the Neovim module for a certain Python major version does
not mean that the tested interpreters are actually of that version.
For example, we test the "python" executable, which is Python 2 on
Ubuntu and Python 3 on Arch Linux.
[1] https://docs.python.org/2/library/pkgutil.html#pkgutil.find_loader
[2] https://docs.python.org/3/library/pkgutil.html#pkgutil.find_loader
[3] https://docs.python.org/3/library/importlib.html#importlib.find_loader
Before, running Nvim in a directory containing a Python module `neovim`,
or one that is imported by it or a plugin, will load that module and not
the system one. So Nvim might be tricked into running arbitrary scripts
from the current working directory.
Fixes#1665Fixes#2530
The executable 'python' can refer to either Python 2 or Python 3. Add a
check to only accept Python 2 interpreters as providers for +python.
Also improve the error messages.
Resolves#2734.
