bpo-35486: Note Py3.6 import system API requirement change (GH-11540)

While the introduction of ModuleNotFoundError was fully backwards
compatible on the import API consumer side, folks providing alternative
implementations of `__import__` need to make an update to be
forward compatible with clients that start relying on the new subclass.



https://bugs.python.org/issue35486

1 files changed, 11 insertions, 0 deletions

diff --git a/Doc/whatsnew/3.6.rst b/Doc/whatsnew/3.6.rst
index 936ea2d..3f5f520 100644
--- a/Doc/whatsnew/3.6.rst
+++ b/Doc/whatsnew/3.6.rst
@@ -2316,6 +2316,17 @@ Changes in the Python API
   a :exc:`DeprecationWarning` in Python 3.6 and a :exc:`RuntimeError` in
   Python 3.8.
 
+* With the introduction of :exc:`ModuleNotFoundError`, import system consumers
+  may start expecting import system replacements to raise that more specific
+  exception when appropriate, rather than the less-specific :exc:`ImportError`.
+  To provide future compatibility with such consumers, implementors of
+  alternative import systems that completely replace :func:`__import__` will
+  need to update their implementations to raise the new subclass when a module
+  can't be found at all. Implementors of compliant plugins to the default
+  import system shouldn't need to make any changes, as the default import
+  system will raise the new subclass when appropriate.
+
+
 Changes in the C API
 --------------------