Index: Python-3.3.0/Lib/unittest/mock.py
===================================================================
--- Python-3.3.0.orig/Lib/unittest/mock.py
+++ Python-3.3.0/Lib/unittest/mock.py
@@ -2163,6 +2163,24 @@ FunctionTypes = (
 
 file_spec = None
 
+def _iterate_read_data(read_data):
+    # Helper for mock_open:
+    # Retrieve lines from read_data via a generator so that separate calls to
+    # readline, read, and readlines are properly interleaved
+    data_as_list = ['{}\n'.format(l) for l in read_data.split('\n')]
+
+    if data_as_list[-1] == '\n':
+        # If the last line ended in a newline, the list comprehension will have an
+        # extra entry that's just a newline.  Remove this.
+        data_as_list = data_as_list[:-1]
+    else:
+        # If there wasn't an extra newline by itself, then the file being
+        # emulated doesn't have a newline to end the last line  remove the
+        # newline that our naive format() added
+        data_as_list[-1] = data_as_list[-1][:-1]
+
+    for line in data_as_list:
+        yield line
 
 def mock_open(mock=None, read_data=''):
     """
@@ -2173,9 +2191,15 @@ def mock_open(mock=None, read_data=''):
     default) then a `MagicMock` will be created for you, with the API limited
     to methods or attributes available on standard file handles.
 
-    `read_data` is a string for the `read` method of the file handle to return.
-    This is an empty string by default.
+    `read_data` is a string for the `read` methoddline`, and `readlines` of the
+    file handle to return.  This is an empty string by default.
     """
+    def _remaining_data_as_list():
+        return list(handle._data)
+
+    def _remaining_data_as_string():
+        return ''.join(handle._data)
+
     global file_spec
     if file_spec is None:
         import _io
@@ -2186,8 +2210,12 @@ def mock_open(mock=None, read_data=''):
 
     handle = MagicMock(spec=file_spec)
     handle.write.return_value = None
+    handle._data = _iterate_read_data(read_data)
     handle.__enter__.return_value = handle
-    handle.read.return_value = read_data
+    handle.read.side_effect = _remaining_data_as_string
+
+    handle.readline.side_effect = handle._data
+    handle.readlines.side_effect = _remaining_data_as_list
 
     mock.return_value = handle
     return mock
Index: Python-3.3.0/Lib/unittest/test/testmock/testwith.py
===================================================================
--- Python-3.3.0.orig/Lib/unittest/test/testmock/testwith.py
+++ Python-3.3.0/Lib/unittest/test/testmock/testwith.py
@@ -171,6 +171,60 @@ class TestMockOpen(unittest.TestCase):
 
         self.assertEqual(result, 'foo')
 
+    def test_readline_data(self):
+        # Check that readline will return all the lines from the fake file
+        mock = mock_open(read_data='foo\nbar\nbaz\n')
+        with patch('%s.open' % __name__, mock, create=True):
+            h = open('bar')
+            line1 = h.readline()
+            line2 = h.readline()
+            line3 = h.readline()
+        self.assertEqual(line1, 'foo\n')
+        self.assertEqual(line2, 'bar\n')
+        self.assertEqual(line3, 'baz\n')
+
+        # Check that we properly emulate a file that doesn't end in a newline
+        mock = mock_open(read_data='foo')
+        with patch('%s.open' % __name__, mock, create=True):
+            h = open('bar')
+            result = h.readline()
+        self.assertEqual(result, 'foo')
+
+    def test_readlines_data(self):
+        # Test that emulating a file that ends in a newline character works
+        mock = mock_open(read_data='foo\nbar\nbaz\n')
+        with patch('%s.open' % __name__, mock, create=True):
+            h = open('bar')
+            result = h.readlines()
+        self.assertEqual(result, ['foo\n', 'bar\n', 'baz\n'])
+
+        # Test that files without a final newline will also be correctly
+        # emulated
+        mock = mock_open(read_data='foo\nbar\nbaz')
+        with patch('%s.open' % __name__, mock, create=True):
+            h = open('bar')
+            result = h.readlines()
+
+        self.assertEqual(result, ['foo\n', 'bar\n', 'baz'])
+
+    def test_interleaved_reads(self):
+        # Test that calling read, readline, and readlines pulls data
+        # sequentially from the data we preload with
+        mock = mock_open(read_data='foo\nbar\nbaz\n')
+        with patch('%s.open' % __name__, mock, create=True):
+            h = open('bar')
+            line1 = h.readline()
+            rest = h.readlines()
+        self.assertEqual(line1, 'foo\n')
+        self.assertEqual(rest, ['bar\n', 'baz\n'])
+
+        mock = mock_open(read_data='foo\nbar\nbaz\n')
+        with patch('%s.open' % __name__, mock, create=True):
+            h = open('bar')
+            line1 = h.readline()
+            rest = h.read()
+        self.assertEqual(line1, 'foo\n')
+        self.assertEqual(rest, 'bar\nbaz\n')
 
 if __name__ == '__main__':
     unittest.main()
Index: Python-3.3.0/Doc/library/unittest.mock.rst
===================================================================
--- Python-3.3.0.orig/Doc/library/unittest.mock.rst
+++ Python-3.3.0/Doc/library/unittest.mock.rst
@@ -1950,8 +1950,12 @@ mock_open
     default) then a `MagicMock` will be created for you, with the API limited
     to methods or attributes available on standard file handles.
 
-    `read_data` is a string for the `read` method of the file handle to return.
-    This is an empty string by default.
+    `read_data` is a string for the `read`, `readline`, and `readlines` methods
+    of the file handle to return.  Calls to those methods will take data from
+    `read_data` until it is depleted.  The mock of these methods is pretty
+    simplistic.  If you need more control over the data that you are feeding to
+    the tested code you will need to customize this mock for yourself.
+    `read_data` is an empty string by default.
 
 Using `open` as a context manager is a great way to ensure your file handles
 are closed properly and is becoming common::