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 )

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.

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.

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.

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

Ok, fair enough.

Yeah, if it isn't comparable it should return either False or NotImplemented, not raise an exception. False would be better here, I think.

It looks like there's a related bug in call_args around __ne__:

>>> m = Mock()
>>> m(1,2)
<Mock name='mock()' id='4483976016'>
>>> m.call_args
call(1, 2)
>>> m.call_args == call(1,2)
True
>>> m.call_args != call(1,2)
True

Any reason not to define __ne__ as not __eq__? Otherwise it looks like you fall back to tuple.__ne__, which does the wrong thing here.

Here's a simple patch + test for the original bug. I'll file the __ne__ question separately.

New changeset 83ea55a1204a by Berker Peksag in branch '3.4':
Issue bpo-24857: Comparing call_args to a long sequence now correctly returns a
https://hg.python.org/cpython/rev/83ea55a1204a

New changeset df91c1879e56 by Berker Peksag in branch '3.5':
Issue bpo-24857: Comparing call_args to a long sequence now correctly returns a
https://hg.python.org/cpython/rev/df91c1879e56

New changeset 6853b4bc0b22 by Berker Peksag in branch 'default':
Issue bpo-24857: Comparing call_args to a long sequence now correctly returns a
https://hg.python.org/cpython/rev/6853b4bc0b22

Thanks!

For the record, the __ne__ issue created by A Kaptur is bpo-24997.