[tahoe-lafs-trac-stream] [Tahoe-LAFS] #2899: ValueOrderedDict throws IndexError when given equal non-identical keys

[Tahoe-LAFS]

#2899: ValueOrderedDict throws IndexError when given equal non-identical keys
--------------------+---------------------------
 Reporter:  warner  |          Owner:
     Type:  defect  |         Status:  new
 Priority:  minor   |      Milestone:  undecided
Component:  code    |        Version:  1.12.1
 Keywords:          |  Launchpad Bug:
--------------------+---------------------------
 {{{
 from allmydata.util.dictutil import ValueOrderedDict
 a = (1,2)
 b = (1,2)
 d = ValueOrderedDict()
 d[a] = 1
 d[b] = 1
 d[b] = 2
 }}}

 gives:
 {{{
   File ".../src/allmydata/util/dictutil.py", line 509, in __setitem__
     while (self.l[i][0] is not oldval) or (self.l[i][1] is not key):
 IndexError: list index out of range
 }}}

 I found this while trying to improve the test coverage, to exercise the `i
 += 1` statement inside that `while` loop. I think the only way to reach it
 is to have keys which are equal but not identical. Python doesn't
 (currently? always?) consolidate equivalent tuples (although I think it'd
 be allowed to), which is one way to hit this case.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/2899>
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