| msg117895 - (view) |
Author: Arnaud Delobelle (arno) |
Date: 2010-10-02 20:35 |
| The pprint function in the python 3.1 pprint module fails when printing a dictionary containing more than one item and with one item being a user-defined type. It seems pprint tries to sort the keys but fails, (maybe because calling __lt__ on a user-defined type doesn't bind its first argument to 'self'? Looking into pprint.py would probably yield the answer). This seems related to issue 3976 but it was fixed in r76389 and r76390. My example below fails in r79147. I'm not in a position to check more recent revisions right now. In Python 2.6, the following works fine: Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56) [GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> from pprint import pprint >>> class A(object): pass ... >>> pprint({A:1, 1:2}) {1: 2, <class __main__.A at 0xb77dc47c>: 1} But in Python 3.1, it fails with the error below: Python 3.1.2 (r312:79147, Apr 15 2010, 12:35:07) [GCC 4.4.3] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>> from pprint import pprint >>> class A: pass ... >>> pprint({A:1, 1:2}) Traceback (most recent call last): File "", line 1, in File "/usr/lib/python3.1/pprint.py", line 55, in pprint printer.pprint(object) File "/usr/lib/python3.1/pprint.py", line 132, in pprint self._format(object, self._stream, 0, 0, {}, 0) File "/usr/lib/python3.1/pprint.py", line 155, in _format rep = self._repr(object, context, level - 1) File "/usr/lib/python3.1/pprint.py", line 242, in _repr self._depth, level) File "/usr/lib/python3.1/pprint.py", line 254, in format return _safe_repr(object, context, maxlevels, level) File "/usr/lib/python3.1/pprint.py", line 296, in _safe_repr items = sorted(object.items(), key=_safe_tuple) File "/usr/lib/python3.1/pprint.py", line 89, in __lt__ rv = self.obj.__lt__(other.obj) TypeError: expected 1 arguments, got 0 |
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| msg118209 - (view) |
Author: Rodrigo Bernardo Pimentel (rbp)  |
Date: 2010-10-08 17:58 |
| FWIW, the problem still occurs on the most recent release31-maint checkout (as of r85323), and does not happen on py3k (3.2a2). |
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| msg118214 - (view) |
Author: Rodrigo Bernardo Pimentel (rbp) |
Date: 2010-10-08 18:51 |
| If I'm understanding this correctly, this fails on 3.1 and not (although, actually, it does) on py3k/3.2 because: * pprint._safe_key.__lt__ checks "rv = self.obj.__lt__(other.obj)" and falls back to id comparison if rv is NotImplemented * If the object passed to _safe_key is a class, self.obj.__lt__ will expect *self* as well as the other object. Therefore the verification above fails with "TypeError: expected 1 arguments, got 0". You can see that pprint works with an instance: >>> pprint.pprint({A(): 1, 1: 2}) {<__main__.A object at 0x8594d4c>: 1, 1: 2} * Finally, this works on py3k *for your example* because, for some reason, on py3k the comparison is being based on the 1 key. That is, the comparison on _safe_key.__lt__ happens to be 1.__lt__(A), instead of A.__lt__(1). Perhaps hashing changed after the 3.1 release? Anyway, py3k still fails when you force the comparison to happen on the class: >>> class B(object): pass ... >>> pprint.pprint({A: 1, B: 2}) Traceback (most recent call last): File "", line 1, in File "/home/rbp/python/dev/py3k/Lib/pprint.py", line 55, in pprint printer.pprint(object) File "/home/rbp/python/dev/py3k/Lib/pprint.py", line 132, in pprint self._format(object, self._stream, 0, 0, {}, 0) File "/home/rbp/python/dev/py3k/Lib/pprint.py", line 155, in _format rep = self._repr(object, context, level - 1) File "/home/rbp/python/dev/py3k/Lib/pprint.py", line 245, in _repr self._depth, level) File "/home/rbp/python/dev/py3k/Lib/pprint.py", line 257, in format return _safe_repr(object, context, maxlevels, level) File "/home/rbp/python/dev/py3k/Lib/pprint.py", line 299, in _safe_repr items = sorted(object.items(), key=_safe_tuple) File "/home/rbp/python/dev/py3k/Lib/pprint.py", line 89, in __lt__ rv = self.obj.__lt__(other.obj) TypeError: expected 1 arguments, got 0 >>> So, basically, the fix on issue 3976 does't (always) work when there are classes as dict keys. I think switching from rv = self.obj.__lt__(other.obj) if rv is NotImplemented: to something like try: rv = self.obj < other.obj except TypeError: rv = (str(type(self.obj)), id(self.obj)) < \ (str(type(other.obj)), id(other.obj)) solves this. Or we can check first whether self.obj is a 'type', but I think it gets convoluted. If anyone can confirm that that's the way to go, I can produce one (though it's a trivial one). Raymond? |
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| msg118227 - (view) |
Author: Amaury Forgeot d'Arc (amaury.forgeotdarc) * |
Date: 2010-10-08 21:38 |
| A simpler change would to replace: rv = self.obj.__lt__(other.obj) with rv = type(self.obj).__lt__(self.obj, other.obj) |
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| msg165790 - (view) |
Author: Florent Xicluna (flox) * |
Date: 2012-07-18 17:26 |
| Confirmed on python 3.2 and 3.3. |
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| msg165817 - (view) |
Author: Anton Barkovsky (anton.barkovsky) * |
Date: 2012-07-18 23:24 |
| Here's a patch with fix and tests. Note that class objects are not comparable and have the same type so they fall back on sorting by id. Should we sort them by name as a special case instead? |
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| msg165999 - (view) |
Author: Roundup Robot (python-dev)  |
Date: 2012-07-21 09:23 |
| New changeset 03cda5360dc6 by Florent Xicluna in branch '3.2': Issues #10017 and #14998: Fix TypeError using pprint on dictionaries with unorderable key. http://hg.python.org/cpython/rev/03cda5360dc6 New changeset 4d0dcfbdf45b by Florent Xicluna in branch 'default': Issues #10017 and #14998: Fix TypeError using pprint on dictionaries with unorderable key. http://hg.python.org/cpython/rev/4d0dcfbdf45b |
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| msg166000 - (view) |
Author: Florent Xicluna (flox) * |
Date: 2012-07-21 09:27 |
| Thanks for this patch. I've reviewed the issue and merged the patch of issue #14998 which fixes both cases. |
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