Cleanup: comments for is_path_builtin

Also reduce scope of import.

release/scripts/modules/bpy/utils/__init__.py

@@ -456,12 +456,19 @@ def preset_paths(subdir):
 
     return dirs
 
+
 def is_path_builtin(path):
     """
-    Returns True if the path in question in one of the built in paths used by blender.
+    Returns True if the path is one of the built-in paths used by Blender.
 
-    :arg path: Path you want to check if it is in the built in settings directory
+    :arg path: Path you want to check if it is in the built-in settings directory
+    :type path: str
+    :rtype: bool
     """
+    # Note that this function is is not optimized for speed,
+    # it's intended to be used to check if it's OK to remove presets.
+    #
+    # If this is used in a draw-loop for example, we could cache some of the values.
     search_path = _os.path.abspath(path)
     user_path = resource_path('USER')
 
@@ -469,15 +476,19 @@ def is_path_builtin(path):
         parent_path = resource_path(res)
         if not parent_path or parent_path == user_path:
             # Make sure that the current path is not empty string and that it is
-            # not the same as the user config path. IE "~/.config/blender" on linux
+            # not the same as the user config path. IE "~/.config/blender" on Linux
             # This can happen on portable installs.
             continue
 
-        if _os.path.samefile(_os.path.commonpath([parent_path]), _os.path.commonpath([parent_path, path])):
+        if _os.path.samefile(
+                _os.path.commonpath([parent_path]),
+                _os.path.commonpath([parent_path, path])
+        ):
             return True
 
     return False
 
+
 def smpte_from_seconds(time, fps=None, fps_base=None):
     """
     Returns an SMPTE formatted string from the *time*: