[Python-Dev] Avoiding error from repr() of recursive dictview (original) (raw)

Jan Kaliszewski zuo at chopin.edu.pl
Tue Jul 23 00:30:12 CEST 2013

23.07.2013 00:01, Gregory P. Smith wrote:

On Mon, Jul 22, 2013 at 2:44 PM, Ben North <ben at redfrontdoor.org> wrote:

A friend of mine, Ruadhan O'Flanagan, came across a bug which turned out to be the one noted in [http://bugs.python.org/issue18019 [1]], i.e.:

>>> d={} >>> d[42]=d.viewvalues() >>> d This issue has been fixed in hg; the behaviour now is that a RuntimeError is produced for a recursive dictionary view: >>> d={} >>> d[42]=d.viewvalues() >>> d # (output line-broken:) {42: Traceback (most recent call last): File "", line 1, in RuntimeError: maximum recursion depth exceeded while getting the repr of a list Before finding this, though, I'd investigated and made a patch which produces a similar "..." output to a recursive dictionary.  Reworking against current 2.7, the behaviour would be: >>> x={} >>> x[42]=x >>> x # existing behaviour for dictionaries: {42: {...}} >>> d={} >>> d[42]=d.viewvalues() >>> d # new behaviour: {42: dictvalues([...])} >>> d[43]=d.viewitems() >>> d # (output line-broken:) {42: dictvalues([..., dictitems([(42, ...), (43, ...)])]),  43: dictitems([(42, dictvalues([..., ...])), (43, ...)])} Attached is the patch, against current 2.7 branch.  If there is interest in applying this, I will create a proper patch (changelog entry, fix to Lib/test/testdictviews.py, etc.). Mailing lists are where patches go to get lost and die. :)  Post it on an issue on bugs.python.org [4].  Given that the RuntimeError fix has been released, your proposed ... behavior is arguably a new feature so I'd only expect this to make sense for consideration in 3.4, not 2.7.  (if accepted at all)

IMHO it's still a bug (even though not so painful as segfault) that should also be fixed in 2.7 and 3.2/3.3.

In other cases (such as d={}; d[42]=d; repr(d)) Python does its best to avoid an error -- why in this case (d={}; d[42]=d.<Py2.x:view>values(); repr(d)) should it raise an exception? IMHO it's an obvious oversight in implementation, not a feature that anybody would expect.

Regards. *j

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