How to specify Python interpreter version in VIM?

You probably don't want to (or at least should not) set python3 as the default python interpreter for vim, as then some (most of) your plugins will become incompatible, such as YouCompleteMe and clang_complete itself, because they do not have python3 support. Normally plugins that do support python3 let you decide if you want to use it by adding to your .vimrc

let g:syntastic_python_python_exec = 'python3' 

Solution: the :echo has('python') showing 0 is actually telling you that vim is perhaps not compiled with python2. So first check the output of vim --version and you should be able to see a list of shared libraries that your compiler has built vim against. Do you see the following? (e.g. for python 2.7):

-L/usr/lib/python2.7/config-x86_64-linux-gnu -lpython2.7

If not (or if you see both -lpython2.x and -lpython3.x I suggest you compile vim from source, linking it specifically to -lpython2.x. It is not that difficult to build vim from source. First make sure to remove all your current vim installation, for instance using aptitude you'd do:

sudo apt-get remove --purge vim vim-runtime vim-gnome vim-tiny vim-common vim-gui-common

clone vim mercurial

hg clone https://code.google.com/p/vim/
cd vim

and then run ./configure with the following flags:

 ./configure --with-features=huge \
        --enable-cscope \
        --enable-pythoninterp \
        --enable-largefile \
        --with-python-config-dir=/usr/lib/python2.7/config 

you might also want to link against ruby and lua if you want, and then finally run

make build
make install

Here is shell script that will automate the whole process for you. This might be a bit of an overkill, but I think this is how you should handle this to not run with compatibility issues with your future packages.