[Zope-dev] Re: Unit Test Failures

[Tim Peters]

...

[Philipp]
>> Well, if you look closer you find that it uses pprint.pformat which
always outputs the
>> same on all machines (because it provides output sorted by the
dictionary key).

[Tres Seaver]
> I see that in the implementation;  it isn't documented as part of
> pprint's contract, however.

It's not part of the implementation either.  For example,

>>> d = {"z": 1, "m": 2}
>>> pprint.pprint(d)
{'z': 1, 'm': 2}

That is, it's not true that pprint always sorts a dict for display. 
Looks like Jim's suggested

    from zope.testing.doctestunit import pprint

inherits this insecurity.

In the example above, two things conspire to give "unsorted" output:

1. pprint(dict) doesn't try to sort at all if _repr(dict) is "short".

2. On my 32-bit box, hash('z') < hash('m'), which leads to platform accidents
   in dict insertion putting 'z' before 'm' in the "natural" dict
iteration order:

>>> d
{'z': 1, 'm': 2}

   Because of #1, pprint passes on that order.

On a 64-bit box, the order may differ (or across Python versions on
one box if the string hash, or dict insertion, algorithms change).