[issue26807] mock_open()().readline() fails at EOF

[Robert Collins]

Robert Collins added the comment:

I've committed a minimal variation - thanks for the patches.

--
resolution:  -> fixed
stage: test needed -> resolved
status: open -> closed

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[issue26807] mock_open()().readline() fails at EOF

[Roundup Robot]

Roundup Robot added the comment:

New changeset cbb31b2a3dba by Robert Collins in branch '3.5':
Issue #26807: mock_open 'files' no longer error on readline at end of file.
https://hg.python.org/cpython/rev/cbb31b2a3dba

New changeset 72a798e27117 by Robert Collins in branch 'default':
Issue #26807: mock_open 'files' no longer error on readline at end of file.
https://hg.python.org/cpython/rev/72a798e27117

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nosy: +python-dev

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[issue26807] mock_open()().readline() fails at EOF

[Robert Collins]

Robert Collins added the comment:

So something like

  for line in _state[0]:
  yield line
  while True:
yield ''

Will probably do it just fine.

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[issue26807] mock_open()().readline() fails at EOF

[Robert Collins]

Robert Collins added the comment:

Actually, further inspection and a teddybear with Angus Lees uncovers this:

diff --git a/Lib/unittest/test/testmock/testmock.py 
b/Lib/unittest/test/testmock/testmock.py
--- a/Lib/unittest/test/testmock/testmock.py
+++ b/Lib/unittest/test/testmock/testmock.py
@@ -1419,6 +1419,18 @@
 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()



 ./python Lib/unittest/test/testmock/testmock.py
..sE
==
ERROR: test_mock_open_after_eof (__main__.MockTest)
--
Traceback (most recent call last):
  File "Lib/unittest/test/testmock/testmock.py", line 1430, in 
test_mock_open_after_eof
self.assertEqual('', h.readline())
  File "/home/robertc/work/cpython-3.5.hg/Lib/unittest/mock.py", line 917, in 
__call__
return _mock_self._mock_call(*args, **kwargs)
  File "/home/robertc/work/cpython-3.5.hg/Lib/unittest/mock.py", line 976, in 
_mock_call
result = next(effect)
StopIteration

--
Ran 80 tests in 0.197s

FAILED (errors=1, skipped=1)


That is, we need the yield '' to be infinite - while True: yield '', or the 
while True: to be outside the try:except.

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[issue26807] mock_open()().readline() fails at EOF

[Robert Collins]

Robert Collins added the comment:

./python Lib/unittest/test/testmock/testmock.py
..s.
--
Ran 80 tests in 0.180s

OK (skipped=1)


So thats great. I am going to have to stare that this quite hard to be sure I 
understand why it fails without the change away from 'for line in ' - but yes, 
this is the right place, and I'll commit it to 3.5 and 3.6 and backport it to 
the external mock tomorrow.

Thanks!

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[issue26807] mock_open()().readline() fails at EOF

[Yolanda]

Yolanda added the comment:

How about...

@@ -2339,9 +2339,12 @@ def mock_open(mock=None, read_data=''):
 if handle.readline.return_value is not None:
 while True:
 yield handle.readline.return_value
-for line in _state[0]:
-yield line
 
+try:
+while True:
+yield next(_state[0])
+except StopIteration:
+yield ''

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[issue26807] mock_open()().readline() fails at EOF

[Yolanda]

Yolanda added the comment:

I tried patching the readline_side_effect call. But i cannot trap StopIteration 
there, and i don't see any clear way to detect that the generator has reached 
its end at that level.

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[issue26807] mock_open()().readline() fails at EOF

[Robert Collins]

Robert Collins added the comment:

You're changing _mock_call but readline is actually implemented in 
_readline_side_effect - just changing that should be all thats needed (to deal 
with StopIteration). You will however need to fixup the return values since the 
test I added is a bit wider than just the single defect you uncovered.

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[issue26807] mock_open()().readline() fails at EOF

[Yolanda]

Yolanda added the comment:

So... the failures are because i'm capturing the StopIteration exception in 
that case. then it's normal that it's not raised. How should you solve that 
problem instead?

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[issue26807] mock_open()().readline() fails at EOF

[Robert Collins]

Robert Collins added the comment:

Thanks Yolanda. I've touched up the test a little and run a full test run (make 
test) - sadly it fails: there is an explicit test that StopIteration gets 
raised if you set it as a side effect.


==
FAIL: test_mock_open_after_eof (unittest.test.testmock.testmock.MockTest)
--
Traceback (most recent call last):
  File "/home/robertc/work/cpython-3.5.hg/Lib/unittest/test/testmock/test   
   mock.py", line 1428, in test_mock_open_after_eof
self.assertEqual('', h.readline())
AssertionError: '' != None

==
FAIL: test_side_effect_iterator (unittest.test.testmock.testmock.MockTest   
   )
--
Traceback (most recent call last):
  File "/home/robertc/work/cpython-3.5.hg/Lib/unittest/test/testmock/test   
   mock.py", line 980, in test_side_effect_iterator
self.assertRaises(StopIteration, mock)
AssertionError: StopIteration not raised by 

==
FAIL: test_side_effect_setting_iterator (unittest.test.testmock.testmock.   
   MockTest)
--
Traceback (most recent call last):
  File "/home/robertc/work/cpython-3.5.hg/Lib/unittest/test/testmock/test   
   mock.py", line 1015, in 
test_side_effect_setting_iterator
self.assertRaises(StopIteration, mock)
AssertionError: StopIteration not raised by 

--
Ran 705 tests in 1.251s

FAILED (failures=3, skipped=3)

Of those, I think the first failure is a bug in the patch; the second and third 
are genuine failures - you'll need to make your change in mock_open itself, not 
in 'mock'.

I've attached an updated patch which has ACKS, NEWS filled out and tweaked your 
test to be more comprehensive.

--
keywords: +patch
Added file: http://bugs.python.org/file42590/issue26807.diff

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[issue26807] mock_open()().readline() fails at EOF

[Yolanda]

Yolanda added the comment:

diff --git a/Lib/unittest/test/testmock/testwith.py 
b/Lib/unittest/test/testmock/testwith.py
index a7bee73..efe6391 100644
--- a/Lib/unittest/test/testmock/testwith.py
+++ b/Lib/unittest/test/testmock/testwith.py
@@ -297,5 +297,16 @@ class TestMockOpen(unittest.TestCase):
 self.assertEqual(handle.readline(), 'bar')
 
 
+def test_readlines_after_eof(self):
+# Check that readlines does not fail after the end of file
+mock = mock_open(read_data='foo')
+with patch('%s.open' % __name__, mock, create=True):
+h = open('bar')
+h.read()
+h.read()
+data = h.readlines()
+self.assertEqual(data, [])
+
+
 if __name__ == '__main__':
 unittest.main()

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[issue26807] mock_open()().readline() fails at EOF

[Robert Collins]

Robert Collins added the comment:

Thanks Yolanda, that looks sane - could you perhaps add a test for this in 
Lib/unittest/tests/test_mock/ ?

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[issue26807] mock_open()().readline() fails at EOF

[Yolanda]

Yolanda added the comment:

diff --git a/Lib/unittest/mock.py b/Lib/unittest/mock.py
index 7400fb7..9e47cd2 100644
--- a/Lib/unittest/mock.py
+++ b/Lib/unittest/mock.py
@@ -991,7 +991,10 @@ class CallableMixin(Base):
 raise effect
 
 if not _callable(effect):
-result = next(effect)
+try:
+result = next(effect)
+except StopIteration:
+result = None
 if _is_exception(result):
 raise result
 if result is DEFAULT:

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nosy: +yolanda.robla

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[issue26807] mock_open()().readline() fails at EOF

[Robert Collins]

New submission from Robert Collins:

>>> import unittest.mock
>>> o = unittest.mock.mock_open(read_data="fred")
>>> f = o()
>>> f.read()
'fred'
>>> f.read()
''
>>> f.readlines()
[]
>>> f.readline()
Traceback (most recent call last):
  File "", line 1, in 
  File "/home/robertc/work/cpython/Lib/unittest/mock.py", line 935, in __call__
return _mock_self._mock_call(*args, **kwargs)
  File "/home/robertc/work/cpython/Lib/unittest/mock.py", line 994, in 
_mock_call
result = next(effect)
StopIteration

--
components: Library (Lib)
messages: 263814
nosy: rbcollins
priority: normal
severity: normal
stage: test needed
status: open
title: mock_open()().readline() fails at EOF
type: behavior
versions: Python 3.5, Python 3.6

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