python - find virtualenv current package directory for vim -

i want able reach source code virtualenv library via ctags able need know virtualenv active, example, have code in .vimrc appends django ctags index:

nnoremap <f7> :!ctags -r --python-kinds=-i -a ~/.virtualenvs/myproject/lib/python2.7/site-packages/django/*<cr> 

instead of hardcoding path want like:

nnoremap <f7> :!ctags -r --python-kinds=-i -a current_project_packages_path/django/* 

so can index packages current project working on.

you use $virtual_env library, it'd this

nnoremap <f7> :!ctags -r --python-kinds=-i -a $virtual_env/lib/python2.7/site-packages/django/*