bpo-33262: Deprecate passing None for s to shlex.split()

Doc/library/shlex.rst

@@ -36,6 +36,9 @@ The :mod:`shlex` module defines the following functions:
       instance, passing ``None`` for *s* will read the string to split from
       standard input.
 
+   .. deprecated:: 3.9
+      Passing ``None`` for *s* will raise an exception in future Python
+      versions.
 
 .. function:: join(split_command)
 

Doc/whatsnew/3.9.rst

@@ -624,6 +624,9 @@ Deprecated
   by :c:func:`Py_Initialize()` since Python 3.7.
   (Contributed by Victor Stinner in :issue:`39877`.)
 
+* Passing ``None`` as the first argument to the :func:`shlex.split` function
+  has been deprecated.  (Contributed by Zackery Spytz in :issue:`33262`.)
+
 
 Removed
 =======

Lib/shlex.py

@@ -304,6 +304,10 @@ def __next__(self):
 
 def split(s, comments=False, posix=True):
     """Split the string *s* using shell-like syntax."""
+    if s is None:
+        import warnings
+        warnings.warn("Passing None for 's' to shlex.split() is deprecated.",
+                      DeprecationWarning, stacklevel=2)
     lex = shlex(s, posix=posix)
     lex.whitespace_split = True
     if not comments:

Lib/test/test_shlex.py

@@ -3,7 +3,7 @@
 import shlex
 import string
 import unittest
-
+from unittest import mock
 
 
 # The original test data set was from shellwords, by Hartmut Goebel.
@@ -162,6 +162,11 @@ def oldSplit(self, s):
             tok = lex.get_token()
         return ret
 
+    @mock.patch('sys.stdin', io.StringIO())
+    def testSplitNoneDeprecation(self):
+        with self.assertWarns(DeprecationWarning):
+            shlex.split(None)
+
     def testSplitPosix(self):
         """Test data splitting with posix parser"""
         self.splitTest(self.posix_data, comments=True)

Misc/NEWS.d/next/Library/2018-04-17-13-23-29.bpo-33262.vHC7YQ.rst

@@ -0,0 +1,2 @@
+Deprecate passing None as an argument for :func:`shlex.split()`'s ``s``
+parameter.  Patch by Zackery Spytz.