[issue10242] unittest's assertItemsEqual() method makes too many assumptions about its input

[Raymond Hettinger]

Raymond Hettinger <rhettinger at users.sourceforge.net> added the comment:

Suggestions:

* new name:  assertCountEqual(a, b)
  or:        assertElementCountEqual(a, b)

  this name captures the essential service:

  - unordered comparison where duplicates matter
  - inputs are "elements", 
    not "items" which means key/value pairs


* O(n) implementation with O(n**2) fallback:

   try:
     a_cnt = collections.Counter(a)
     b_cnt = collections.Counter(b)
   except TypeError:
     # do current O(n**2) fallback
   else:
       if a_cnt == b_cnt:
          # test passed
       else:
          in_a_but_not_in_b = a - b
          in_b_but_not_in_a = b - a
          # display nice diff

* documentation should emphasize the new name:

  assertElementCountEqual(a, b)
  obsolete alias:  assertItemsEqual(a, b)

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assignee: rhettinger -> michael.foord

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue10242>
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