bpo-32933: Implement dunder iter method on mock_open

Doc/library/unittest.mock.rst

@@ -2095,6 +2095,10 @@ mock_open
  .. versionchanged:: 3.5
  *read_data* is now reset on each call to the *mock*.
 
+ .. versionchanged:: 3.8
+ Added :meth:`__iter__` to implementation so that iteration (such as in for
+ loops) correctly consumes *read_data*.
+
 Using :func:`open` as a context manager is a great way to ensure your file handles
 are closed properly and is becoming common::
 

Lib/unittest/mock.py

@@ -2356,14 +2356,16 @@ def _read_side_effect(*args, **kwargs):
  return type(read_data)().join(_state[0])
 
  def _readline_side_effect():
+ yield from _iter_side_effect()
+ while True:
+ yield type(read_data)()
+
+ def _iter_side_effect():
  if handle.readline.return_value is not None:
  while True:
  yield handle.readline.return_value
  for line in _state[0]:
  yield line
- while True:
- yield type(read_data)()
-
 
  global file_spec
  if file_spec is None:
@@ -2387,6 +2389,7 @@ def _readline_side_effect():
  _state[1] = _readline_side_effect()
  handle.readline.side_effect = _state[1]
  handle.readlines.side_effect = _readlines_side_effect
+ handle.__iter__.side_effect = _iter_side_effect
 
  def reset_data(*args, **kwargs):
  _state[0] = _iterate_read_data(read_data)

Lib/unittest/test/testmock/testmock.py

@@ -1450,6 +1450,16 @@ def test_mock_open_reuse_issue_21750(self):
  f2_data = f2.read()
  self.assertEqual(f1_data, f2_data)
 
+ def test_mock_open_dunder_iter_issue(self):
+ # Test dunder_iter method generates the expected result and
+ # consumes the iterator.
+ mocked_open = mock.mock_open(read_data='Remarkable\nNorwegian Blue')
+ f1 = mocked_open('a-name')
+ lines = [line for line in f1]
+ self.assertEqual(lines[0], 'Remarkable\n')
+ self.assertEqual(lines[1], 'Norwegian Blue')
+ self.assertEqual(list(f1), [])
+
  def test_mock_open_write(self):
  # Test exception in file writing write()
  mock_namedtemp = mock.mock_open(mock.MagicMock(name='JLV'))

Lib/unittest/test/testmock/testwith.py

@@ -188,6 +188,7 @@ def test_read_data(self):
 
  def test_readline_data(self):
  # Check that readline will return all the lines from the fake file
+ # And that once fully consumed, readline will return an empty string.
  mock = mock_open(read_data='foo\nbar\nbaz\n')
  with patch('%s.open' % __name__, mock, create=True):
  h = open('bar')
@@ -197,13 +198,27 @@ def test_readline_data(self):
  self.assertEqual(line1, 'foo\n')
  self.assertEqual(line2, 'bar\n')
  self.assertEqual(line3, 'baz\n')
+ self.assertEqual(h.readline(), '')
 
  # 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')
+ self.assertEqual(h.readline(), '')
+
+
+ def test_dunder_iter_data(self):
+ # Check that dunder_iter 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')
+ lines = [l for l in h]
+ self.assertEqual(lines[0], 'foo\n')
+ self.assertEqual(lines[1], 'bar\n')
+ self.assertEqual(lines[2], 'baz\n')
+ self.assertEqual(h.readline(), '')
 
 
  def test_readlines_data(self):

Misc/NEWS.d/next/Library/2018-04-30-22-43-31.bpo-32933.M3iI_y.rst

@@ -0,0 +1,2 @@
+:func:`unittest.mock.mock_open` now supports iteration over the file
+contents. Patch by Tony Flury.