Properly detect Django (well, availability of pylint-django)

.vim/after/ftplugin/python.vim

@@ -0,0 +1,40 @@
+python3 <<EOF
+import vim
+from importlib.util import find_spec
+import os
+import glob
+
+def find_virtualenv(virtualenv_names):
+    cwd = vim.eval('getcwd()')
+    while cwd != '/':
+        for virtualenv_name in virtualenv_names:
+            venv_path = os.path.join(cwd, virtualenv_name)
+            if os.path.exists(venv_path):
+                return venv_path
+
+        cwd, _ignored = os.path.split(cwd)
+
+    return os.environ.get('VIRTUAL_ENV')
+
+# If we have a virtualenv, check to see whether it contains pylint and the
+# django module. If we don't, just try to import both.  We can't even use
+# ale's "ale_virtualenv_dir_names" here, because it's not set yet.
+
+virtualenv_path = find_virtualenv(['virtualenv', 'venv'])  #vim.eval('ale_virtualenv_dir_names')
+
+if virtualenv_path:
+    has_pylint_django = glob.glob(os.path.join(virtualenv_path, 'lib/*/site-packages/pylint_django'))
+else:
+    try:
+        find_spec('pylint_django')
+        has_pylint_django = True
+    except ImportError:
+        has_pylint_django = False
+
+if has_pylint_django:
+    # No silly 80-char line limit. Sorry pep-8. Also, Django support. Disable 'invalid name', 'missing docstring'
+    vim.command("let g:ale_python_pylint_options='--max-line-length=120 --load-plugins pylint_django --disable=invalid-name,missing-docstring'")
+else:
+    # No silly 80-char line limit. Sorry pep-8. Disable 'invalid name', 'missing docstring'
+    vim.command("let g:ale_python_pylint_options='--max-line-length=120 --disable=invalid-name,missing-docstring'")
+EOF

.vimrc

@@ -313,11 +313,8 @@ let g:ale_fixers = {}
 " Python specific settings
 let g:ale_fixers.python = ['isort']
 " No silly 80-char line limit. Sorry pep-8. Also, Django support. Disable 'invalid name', 'missing docstring'
-if exists('b:is_django')
+"let g:ale_python_pylint_options="--max-line-length=120 --disable=invalid-name,missing-docstring"
-    let g:ale_python_pylint_options="--max-line-length=120 --load-plugins pylint_django --disable=invalid-name,missing-docstring"
+" VIMHOME/after/ftplugin/python.vim takes care of this
-else
-    let g:ale_python_pylint_options="--max-line-length=120 --disable=invalid-name,missing-docstring"
-endif
 " Show errors or warnings in the statusline
 let g:airline#extensions#ale#enabled = 1
 " UI