bpo-40486: Specify what happens if directory content change diring iteration

Doc/library/glob.rst

@@ -43,7 +43,9 @@ For example, ``'[?]'`` matches the character ``'?'``.
    (like :file:`/usr/src/Python-1.5/Makefile`) or relative (like
    :file:`../../Tools/\*/\*.gif`), and can contain shell-style wildcards. Broken
    symlinks are included in the results (as in the shell). Whether or not the
-   results are sorted depends on the file system.
+   results are sorted depends on the file system.  If a file that satisfies
+   conditions is removed or added during the call of this function, whether
+   a path name for that file be included is unspecified.
 
    If *root_dir* is not ``None``, it should be a :term:`path-like object`
    specifying the root directory for searching.  It has the same effect on

Doc/library/os.rst

@@ -1852,6 +1852,8 @@ features:
    Return a list containing the names of the entries in the directory given by
    *path*.  The list is in arbitrary order, and does not include the special
    entries ``'.'`` and ``'..'`` even if they are present in the directory.
+   If a file is removed from or added to the directory during the call of
+   this function, whether a name for that file be included is unspecified.
 
    *path* may be a :term:`path-like object`.  If *path* is of type ``bytes``
    (directly or indirectly through the :class:`PathLike` interface),
@@ -2257,7 +2259,9 @@ features:
    Return an iterator of :class:`os.DirEntry` objects corresponding to the
    entries in the directory given by *path*. The entries are yielded in
    arbitrary order, and the special entries ``'.'`` and ``'..'`` are not
-   included.
+   included.  If a file is removed from or added to the directory after
+   creating the iterator, whether an entry for that file be included is
+   unspecified.
 
    Using :func:`scandir` instead of :func:`listdir` can significantly
    increase the performance of code that also needs file type or file
@@ -3007,7 +3011,10 @@ features:
    *filenames* is a list of the names of the non-directory files in *dirpath*.
    Note that the names in the lists contain no path components.  To get a full path
    (which begins with *top*) to a file or directory in *dirpath*, do
-   ``os.path.join(dirpath, name)``.
+   ``os.path.join(dirpath, name)``.  Whether or not the lists are sorted
+   depends on the file system.  If a file is removed from or added to the
+   *dirpath* directory during generating the lists, whether a name for that
+   file be included is unspecified.
 
    If optional argument *topdown* is ``True`` or not specified, the triple for a
    directory is generated before the triples for any of its subdirectories

Doc/library/pathlib.rst

@@ -890,6 +890,11 @@ call fails (for example because the path doesn't exist).
       PosixPath('docs/_static')
       PosixPath('docs/Makefile')
 
+   The children are yielded in arbitrary order, and the special entries
+   ``'.'`` and ``'..'`` are not included.  If a file is removed from or added
+   to the directory after creating the iterator, whether an path object for
+   that file be included is unspecified.
+
 .. method:: Path.lchmod(mode)
 
    Like :meth:`Path.chmod` but, if the path points to a symbolic link, the