Closes issue #14982: Document that pkgutil's walk_packages() and

iter_modules() requires iter_modules() be defined on an importer. The
importers in importlib do not define this non-standard method.

Doc/library/pkgutil.rst

@@ -138,6 +138,10 @@ support.
 
    *prefix* is a string to output on the front of every module name on output.
 
+   .. note::
+      Only works for importers which define a ``iter_modules()`` method, which
+      is non-standard but implemented by classes defined in this module.
+
 
 .. function:: walk_packages(path=None, prefix='', onerror=None)
 
@@ -166,6 +170,10 @@ support.
       # list all submodules of ctypes
       walk_packages(ctypes.__path__, ctypes.__name__ + '.')
 
+   .. note::
+      Only works for importers which define a ``iter_modules()`` method, which
+      is non-standard but implemented by classes defined in this module.
+
 
 .. function:: get_data(package, resource)
 

Misc/NEWS

@@ -24,6 +24,10 @@ Core and Builtins
 Library
 -------
 
+- Issue #14982: Document that pkgutil's iteration functions require the
+  non-standard iter_modules() method to be defined by an importer (something
+  the importlib importers do not define).
+
 - Issue #15036: Allow removing or changing multiple items in
   single-file mailboxes (mbox, MMDF, Babyl) flushing the mailbox
   between the changes.