Issue #26807: mock_open 'files' no longer error on readline at end of file.

Patch from Yolanda Robla.

Lib/unittest/mock.py

@@ -2341,6 +2341,8 @@ def _readline_side_effect():
                 yield handle.readline.return_value
         for line in _state[0]:
             yield line
+        while True:
+            yield type(read_data)()
 
 
     global file_spec

Lib/unittest/test/testmock/testmock.py

@@ -1440,6 +1440,18 @@ def test_mock_open_alter_readline(self):
         self.assertEqual('abc', first)
         self.assertEqual('abc', second)
 
+    def test_mock_open_after_eof(self):
+        # read, readline and readlines should work after end of file.
+        _open = mock.mock_open(read_data='foo')
+        h = _open('bar')
+        h.read()
+        self.assertEqual('', h.read())
+        self.assertEqual('', h.read())
+        self.assertEqual('', h.readline())
+        self.assertEqual('', h.readline())
+        self.assertEqual([], h.readlines())
+        self.assertEqual([], h.readlines())
+
     def test_mock_parents(self):
         for Klass in Mock, MagicMock:
             m = Klass()

Misc/ACKS

@@ -1231,6 +1231,7 @@ Ben Roberts
 Mark Roberts
 Andy Robinson
 Jim Robinson
+Yolanda Robla
 Daniel Rocco
 Mark Roddy
 Kevin Rodgers

Misc/NEWS

@@ -290,6 +290,9 @@ Library
 - Issue #22274: In the subprocess module, allow stderr to be redirected to
   stdout even when stdout is not redirected.  Patch by Akira Li.
 
+- Issue #26807: mock_open 'files' no longer error on readline at end of file.
+  Patch from Yolanda Robla.
+
 - Issue #25745: Fixed leaking a userptr in curses panel destructor.
 
 - Issue #26977: Removed unnecessary, and ignored, call to sum of squares helper