unittest.mock.patch.stopall intermittently doesn't work when the same thing is patched multiple times

[voidspace]

BPO	21239
Nosy	@voidspace

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

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GitHub fields:

assignee = 'https://github.com/voidspace'
closed_at = <Date 2014-04-15.21:22:29.474>
created_at = <Date 2014-04-15.15:54:31.458>
labels = ['type-bug']
title = "unittest.mock.patch.stopall intermittently doesn't work when the same thing is patched multiple times"
updated_at = <Date 2014-04-15.21:22:29.472>
user = 'https://github.com/voidspace'

bugs.python.org fields:

activity = <Date 2014-04-15.21:22:29.472>
actor = 'python-dev'
assignee = 'michael.foord'
closed = True
closed_date = <Date 2014-04-15.21:22:29.474>
closer = 'python-dev'
components = []
creation = <Date 2014-04-15.15:54:31.458>
creator = 'michael.foord'
dependencies = []
files = []
hgrepos = []
issue_num = 21239
keywords = []
message_count = 2.0
messages = ['216322', '216388']
nosy_count = 2.0
nosy_names = ['michael.foord', 'python-dev']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue21239'
versions = ['Python 3.4', 'Python 3.5']

[voidspace]

stopall does not always stop all patches to single target
http://code.google.com/p/mock/issues/detail?id=226

What steps will reproduce the problem?

python code to reproduce error

import mock

def myfunc():
   return 'hello'

m = mock.patch('__main__.myfunc').start()
m.return_value = 'firstmock'
myfunc()

m2 = mock.patch('__main__.myfunc').start()
m2.return_value = 'secondmock'
myfunc()

mock.patch.stopall()
myfunc()

What is the expected output? What do you see instead?
I would expect the output from above to be:
'firstmock'
'secondmock'
'hello'

Instead, sometimes it comes out as:
'firstmock'
'secondmock'
'firstmock'

This result is non-deterministic though so it may also come out as expected. Re-run several times to get the error.

This is a result of using a set to store the active patches. Conversion from a set to a list is non-deterministic because the set has no notion of order.

Please provide any additional information below.

This use case may seem strange, but it shows up in large unit tests where a base class sets up a default patch to catch external calls or something similar and then an individual unit test requiring specific mock behavior patches it differently.

I have a patch here that fixes the problem using a list to store the patches to maintain order and call them in reverse order to stop them in the correct order.

https://code.google.com/r/blak111-mockfix/source/detail?r=3c2f72b0253075d628afb333a79b7cb118132294

[python-dev]

New changeset 727b7e9c40e3 by Michael Foord in branch '3.4':
Closes bpo-21239. unittest.mock.patch.stopall() did not work deterministically when the same name was patched multiple times.
http://hg.python.org/cpython/rev/727b7e9c40e3