New issue 718: Failure to create representation with sets having "unsortable"
elements
https://bitbucket.org/pytest-dev/pytest/issue/718/failure-to-create-representation-with-sets
Edison Gustavo Muenz:
I’m using Python 2.7.7 (The error also happens on Python 2.7.9)
The following code fails:
```python
def test_pretty_printer_screws_up_representation():
class UnsortableKey(object):
def __init__(self, name):
self.name = name
def __lt__(self, other):
raise RuntimeError()
def __repr__(self):
return self.name
def __hash__(self):
return hash(self.name)
def __eq__(self, other):
return self.name == other.name
assert {UnsortableKey('1'), UnsortableKey('2')} == {UnsortableKey('2')}
> assert {UnsortableKey('1'), UnsortableKey('2')} == {UnsortableKey('2')}
E assert set([1, 2]) == set([2])
E (pytest_assertion plugin: representation of details failed. Probably
an object has a faulty __repr__.)
E
X:\etk\coilib50\source\python\coilib50\_pytest\_tests\pytest_almost_equal.py:766:
RuntimeError
```
While debugging, the problem happens in this
[line](https://github.com/python/cpython/blob/2.7/Lib/pprint.py#L199) of
pprint.py (The [PrettyPrinter
module](https://docs.python.org/2/library/pprint.html)).
It assumes that the “object” can have the method sorted() called on it, which
is not always true. The `repr.py` module handles this correctly, but
`pprint.py` doesn’t.
This is the full [traceback](http://pastebin.com/t9a9amcR) (I printed it from
the the `__lt__()` method).
I think that this should be handled by `pprint.py`, however, it is tied to the
python version being used. Maybe pytest could handle this as a workaround this
limitation of `pprint.py`?
Fixing it in `pprint.py` looks straightforward: just handle it like `repr.py`
[does](https://hg.python.org/cpython/file/2.7/Lib/repr.py#l122), by using the
`_possiblysorted()` method.
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