mock: Crash on comparing call_args with long strings

[wilfred]

BPO	24857
Nosy	@bitdancer, @voidspace, @berkerpeksag, @Wilfred
Files	issue24857.patch

^{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 = None
closed_at = <Date 2015-09-09.20:45:21.975>
created_at = <Date 2015-08-13.08:34:40.989>
labels = ['easy', 'type-bug', 'library']
title = 'mock: Crash on comparing call_args with long strings'
updated_at = <Date 2015-09-09.20:45:21.973>
user = 'https://github.com/wilfred'

bugs.python.org fields:

activity = <Date 2015-09-09.20:45:21.973>
actor = 'berker.peksag'
assignee = 'none'
closed = True
closed_date = <Date 2015-09-09.20:45:21.975>
closer = 'berker.peksag'
components = ['Library (Lib)']
creation = <Date 2015-08-13.08:34:40.989>
creator = 'Wilfred.Hughes'
dependencies = []
files = ['40348']
hgrepos = []
issue_num = 24857
keywords = ['patch', 'easy']
message_count = 11.0
messages = ['248504', '248508', '248509', '248510', '248511', '248512', '248517', '249709', '249710', '250333', '250334']
nosy_count = 6.0
nosy_names = ['r.david.murray', 'michael.foord', 'python-dev', 'berker.peksag', 'akaptur', 'Wilfred.Hughes']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue24857'
versions = ['Python 3.4', 'Python 3.5', 'Python 3.6']

[wilfred]

What steps will reproduce the problem?

>>> from mock import Mock
>>> m = Mock()
>>> m(1, 2)
<Mock name='mock()' id='139781492681104'>
>>> m.call_args == "foob"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/wilfred/.py_envs/trifle/lib/python2.7/site-packages/mock.py", line 2061, in __eq__
    first, second = other
ValueError: too many values to unpack

What is the expected output? What do you see instead?

Expected False, got an error instead.

(Migrated from testing-cabal/mock#232 )

[voidspace]

call_args is not user settable! It is set for you by the mock when it is called. Arguably it could be a property instead.

[voidspace]

Oops, I misunderstood the bug report - however, call_args is a tuple, so you can't compare it directly to a string like that. Please refer to the docs on using call_args.

[wilfred]

This caught me by surprise and I spent a while debugging due to this issue. Isn't it reasonable that I can compare two values in Python without exceptions being raised?

>>> (1, 2) == "foob"
False

I'm happy to write a patch.

[wilfred]

This bug is particularly subtle because it only applies to *long* strings.

>>> m.call_args == "f"
False
>>> m.call_args == "fo"
False
>>> m.call_args == "foo"
False
>>> m.call_args == "foob"
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "build/bdist.linux-x86_64/egg/mock.py", line 2061, in __eq__
ValueError: too many values to unpack

[voidspace]

Ok, fair enough.