New submission from Erick Tryzelaar <[EMAIL PROTECTED]>:
I've run into a case where pprint isn't able to print out a particular
data structure, and have distilled it down to a simple example:
import pprint
class A:
pass
pprint.pprint({A(): 1, A(): 2})
Which throws this exception:
Traceback (most recent call last):
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.0/lib/python3
.0/pprint.py", line 272, in _safe_repr
items = sorted(items)
TypeError: unorderable types: A() < A()
During handling of the above exception, another exception occurred:
Traceback (most recent call last):
File "foo.py", line 6, in <module>
pprint.pprint({A(): 1, A(): 2})
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.0/lib/python3
.0/pprint.py", line 55, in pprint
printer.pprint(object)
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.0/lib/python3
.0/pprint.py", line 106, in pprint
self._format(object, self._stream, 0, 0, {}, 0)
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.0/lib/python3
.0/pprint.py", line 129, in _format
rep = self._repr(object, context, level - 1)
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.0/lib/python3
.0/pprint.py", line 216, in _repr
self._depth, level)
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.0/lib/python3
.0/pprint.py", line 228, in format
return _safe_repr(object, context, maxlevels, level)
File
"/opt/local/Library/Frameworks/Python.framework/Versions/3.0/lib/python3
.0/pprint.py", line 277, in _safe_repr
items = sorted(items, key=sortkey)
TypeError: unorderable types: A() < A()
This is happening because of this block of code:
try:
items = sorted(items)
except TypeError:
def sortkey(item):
key, value = item
return str(type(key)), key, value
items = sorted(items, key=sortkey)
The exception block is trying to sort the items again, but in this
instance, it's still not orderable. Could we get _safe_repr to at least
give up on sorting at this point? Or, we could try just falling back to
sorting according to the class name, with:
try:
items = sorted(items)
except TypeError:
def sortkey(item):
key, value = item
return str(type(key)), key, value
try:
items = sorted(items, key=sortkey)
except TypeError:
def sortkey(item):
key, value = item
return str(type(key))
That would at least give some ordering to the output. Unfortunately, in
this case it's a shame that we don't have the cmp function any more,
because then we could just fall back to giving up on the ordering for
just certain unorderable keys, but still have sorted output for
orderable keys. I thought maybe we could test if the key and value have
__lt__, but it looks like all classes now have that function, even if
the user didn't implement it. In the long run though, I suppose the case
where you have mixed types in a dict there's no sensible ordering
anyway.
----------
components: Library (Lib)
messages: 73858
nosy: erickt
severity: normal
status: open
title: pprint._safe_repr is not general enough in one instance
versions: Python 3.0
_______________________________________
Python tracker <[EMAIL PROTECTED]>
<http://bugs.python.org/issue3976>
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