From 704a33d2cf91f34580e4a4abfeb29ffcc2da5412 Mon Sep 17 00:00:00 2001
From: Daniel Hahler <git@thequod.de>
Date: Sat, 17 Nov 2018 23:47:32 +0100
Subject: [PATCH 1/2] Cmd.complete: use completedefault also with cmd=None

Otherwise it will trigger a TypeError ("must be str, not NoneType") below with:

    compfunc = getattr(self, 'complete_' + cmd)

The doc for `parseline` states:

> 'command' and 'args' may be None if the line couldn't be parsed.
---
 Lib/cmd.py                                    |  2 +-
 Lib/test/test_cmd.py                          | 23 +++++++++++++++++++
 .../2019-01-11-12-20-48.bpo-35270.Vtm5iW.rst  |  1 +
 3 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 Misc/NEWS.d/next/Library/2019-01-11-12-20-48.bpo-35270.Vtm5iW.rst

diff --git a/Lib/cmd.py b/Lib/cmd.py
index 859e91096d8f57..cf5952c52ce78a 100644
--- a/Lib/cmd.py
+++ b/Lib/cmd.py
@@ -263,7 +263,7 @@ def complete(self, text, state):
             endidx = readline.get_endidx() - stripped
             if begidx>0:
                 cmd, args, foo = self.parseline(line)
-                if cmd == '':
+                if not cmd:
                     compfunc = self.completedefault
                 else:
                     try:
diff --git a/Lib/test/test_cmd.py b/Lib/test/test_cmd.py
index 96e0c30da328cf..3e2e6351919edf 100644
--- a/Lib/test/test_cmd.py
+++ b/Lib/test/test_cmd.py
@@ -9,6 +9,13 @@
 import unittest
 import io
 from test import support
+from unittest.mock import patch
+
+try:
+    import readline
+except ImportError:
+    readline = None
+
 
 class samplecmdclass(cmd.Cmd):
     """
@@ -218,6 +225,22 @@ def test_input_reset_at_EOF(self):
              "(Cmd) \n"
              "(Cmd) *** Unknown syntax: EOF\n"))
 
+    @unittest.skipIf(readline is None, 'No readline module')
+    @patch('readline.get_line_buffer', return_value='foo')
+    @patch('readline.get_begidx', return_value=2)
+    @patch('readline.get_endidx', return_value=2)
+    def test_complete_with_None_from_parseline(self, *args):
+
+        class CustomCmd(cmd.Cmd):
+            def parseline(self, line):
+                return None, None, line
+
+            def completedefault(self, *args):
+                return ['via_completedefault']
+
+        c = CustomCmd()
+        self.assertEqual(c.complete("", 0), "via_completedefault")
+
 
 def test_main(verbose=None):
     from test import test_cmd
diff --git a/Misc/NEWS.d/next/Library/2019-01-11-12-20-48.bpo-35270.Vtm5iW.rst b/Misc/NEWS.d/next/Library/2019-01-11-12-20-48.bpo-35270.Vtm5iW.rst
new file mode 100644
index 00000000000000..2800b407b48a74
--- /dev/null
+++ b/Misc/NEWS.d/next/Library/2019-01-11-12-20-48.bpo-35270.Vtm5iW.rst
@@ -0,0 +1 @@
+Cmd.complete: use ``completedefault`` also with ``cmd=None`` returned from ``parseline``.

From 28acdbae4fe0c4855fa4336bea97a0a7de3ae45f Mon Sep 17 00:00:00 2001
From: Daniel Hahler <git@thequod.de>
Date: Mon, 11 Mar 2019 15:07:17 +0100
Subject: [PATCH 2/2] update news

---
 .../next/Library/2019-01-11-12-20-48.bpo-35270.Vtm5iW.rst       | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Misc/NEWS.d/next/Library/2019-01-11-12-20-48.bpo-35270.Vtm5iW.rst b/Misc/NEWS.d/next/Library/2019-01-11-12-20-48.bpo-35270.Vtm5iW.rst
index 2800b407b48a74..9a4945e37c71bd 100644
--- a/Misc/NEWS.d/next/Library/2019-01-11-12-20-48.bpo-35270.Vtm5iW.rst
+++ b/Misc/NEWS.d/next/Library/2019-01-11-12-20-48.bpo-35270.Vtm5iW.rst
@@ -1 +1 @@
-Cmd.complete: use ``completedefault`` also with ``cmd=None`` returned from ``parseline``.
+Cmd.complete: use ``completedefault`` also with ``cmd=None`` returned from ``parseline``. Patch contributed by Daniel Hahler.