bpo-31855: unittest.mock.mock_open() results now respects the argument of read([size])

Lib/unittest/mock.py

@@ -25,6 +25,7 @@
 __version__ = '1.0'
 
 
+import io
 import inspect
 import pprint
 import sys
@@ -2346,25 +2347,12 @@ def __init__(self, spec, spec_set=False, parent=None,
 
 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
- sep = b'\n' if isinstance(read_data, bytes) else '\n'
- data_as_list = [l + sep for l in read_data.split(sep)]
-
- if data_as_list[-1] == sep:
- # 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 _to_stream(read_data):
+ if isinstance(read_data, bytes):
+ return io.BytesIO(read_data)
+ else:
+ return io.StringIO(read_data)
 
 
 def mock_open(mock=None, read_data=''):
@@ -2379,20 +2367,23 @@ def mock_open(mock=None, read_data=''):
  `read_data` is a string for the `read`, `readline` and `readlines` of the
  file handle to return. This is an empty string by default.
  """
+ _read_data = _to_stream(read_data)
+ _state = [_read_data, None]
+
  def _readlines_side_effect(*args, **kwargs):
  if handle.readlines.return_value is not None:
  return handle.readlines.return_value
- return list(_state[0])
+ return _state[0].readlines(*args, **kwargs)
 
  def _read_side_effect(*args, **kwargs):
  if handle.read.return_value is not None:
  return handle.read.return_value
- return type(read_data)().join(_state[0])
+ return _state[0].read(*args, **kwargs)
 
- def _readline_side_effect():
+ def _readline_side_effect(*args, **kwargs):
  yield from _iter_side_effect()
  while True:
- yield type(read_data)()
+ yield _state[0].readline(*args, **kwargs)
 
  def _iter_side_effect():
  if handle.readline.return_value is not None:
@@ -2412,8 +2403,6 @@ def _iter_side_effect():
  handle = MagicMock(spec=file_spec)
  handle.__enter__.return_value = handle
 
- _state = [_iterate_read_data(read_data), None]
-
  handle.write.return_value = None
  handle.read.return_value = None
  handle.readline.return_value = None
@@ -2426,7 +2415,7 @@ def _iter_side_effect():
  handle.__iter__.side_effect = _iter_side_effect
 
  def reset_data(*args, **kwargs):
- _state[0] = _iterate_read_data(read_data)
+ _state[0] = _to_stream(read_data)
  if handle.readline.side_effect == _state[1]:
  # Only reset the side effect if the user hasn't overridden it.
  _state[1] = _readline_side_effect()

Lib/unittest/test/testmock/testwith.py

@@ -286,7 +286,12 @@ def test_mock_open_read_with_argument(self):
  # for mocks returned by mock_open
  some_data = 'foo\nbar\nbaz'
  mock = mock_open(read_data=some_data)
- self.assertEqual(mock().read(10), some_data)
+ self.assertEqual(mock().read(10), some_data[:10])
+ self.assertEqual(mock().read(10), some_data[:10])
+
+ f = mock()
+ self.assertEqual(f.read(10), some_data[:10])
+ self.assertEqual(f.read(10), some_data[10:])
 
 
  def test_interleaved_reads(self):

Misc/NEWS.d/next/Library/2019-01-11-17-09-15.bpo-31855.PlhfsX.rst

@@ -0,0 +1,2 @@
+:func:`unittest.mock.mock_open` results now respects the argument of read([size]).
+Patch contributed by Rémi Lapeyre.