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Groups > comp.lang.python > #67060

Re: intersection, union, difference, symmetric difference for dictionaries

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On 2014-02-25 14:40, Skip Montanaro wrote:
> What's the correct result of evaluating this expression?
> 
> {'A': 1} | {'A': 2}
> 
> I can see (at least) two possible "correct" answers.

I would propose at least four:

  {'A': 1}   # choose the LHS
  {'A': 2}   # choose the RHS
  {'A': (1,2)} # a resulting pair of both
  set(['A']) # you did set-ops, so you get a set

If dicts were to support set ops, the last one would be my preferred
result.

I just had to perform set operations on a pair of dicts earlier this
week, shrugged, and did things the manual/explicit way:

  a_dict = dict(...)
  b_dict = dict(...)
  a_set = set(a_dict)
  b_set = set(b_dict)
  added_keys = b_set - a_set
  removed_keys = a_set - b_set
  same_keys = a_set & b_set
  diff_keys = a_set ^ b_set
  all_keys = a_set | b_set

It would save some space if I didn't have to duplicate all the keys
into sets (on the order of 10-100k small strings), instead being able
to directly perform the set-ops on the dicts.  But otherwise, it was
pretty readable & straight-forward.

-tkc

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intersection, union, difference, symmetric difference for dictionaries mauro <mauro@gmail.com> - 2014-02-25 20:32 +0000
  Re: intersection, union, difference, symmetric difference for dictionaries Nick Timkovich <prometheus235@gmail.com> - 2014-02-25 14:37 -0600
  Re: intersection, union, difference, symmetric difference for dictionaries Skip Montanaro <skip@pobox.com> - 2014-02-25 14:40 -0600
  Re: intersection, union, difference, symmetric difference for dictionaries Peter Otten <__peter__@web.de> - 2014-02-25 21:53 +0100
  Re: intersection, union, difference, symmetric difference for dictionaries Peter Otten <__peter__@web.de> - 2014-02-25 21:58 +0100
  Re: intersection, union, difference, symmetric difference for dictionaries Tim Chase <python.list@tim.thechases.com> - 2014-02-25 15:03 -0600
    Re: intersection, union, difference, symmetric difference for dictionaries Duncan Booth <duncan.booth@invalid.invalid> - 2014-02-25 22:21 +0000
      Re: intersection, union, difference, symmetric difference for dictionaries Tim Chase <tim@thechases.com> - 2014-02-25 16:35 -0600
      Re: intersection, union, difference, symmetric difference for dictionaries Tim Chase <python.list@tim.thechases.com> - 2014-02-25 16:36 -0600
      Re: intersection, union, difference, symmetric difference for dictionaries Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2014-02-25 22:58 +0000
    Re: intersection, union, difference, symmetric difference for dictionaries Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-25 23:10 +0000
      Re: intersection, union, difference, symmetric difference for dictionaries Tim Chase <python.list@tim.thechases.com> - 2014-02-25 20:21 -0600
  Re: intersection, union, difference, symmetric difference for dictionaries Ben Finney <ben+python@benfinney.id.au> - 2014-02-26 08:27 +1100
  Re:intersection, union, difference, symmetric difference for dictionaries Dave Angel <davea@davea.name> - 2014-02-25 16:35 -0500
  Re: intersection, union, difference, symmetric difference for dictionaries Peter Otten <__peter__@web.de> - 2014-02-25 22:54 +0100
  Re: intersection, union, difference, symmetric difference for dictionaries mauro <mauro@gmail.com> - 2014-02-25 22:02 +0000
  Re: intersection, union, difference, symmetric difference for dictionaries mauro <mauro@gmail.com> - 2014-02-25 22:03 +0000
  Re: intersection, union, difference, symmetric difference for dictionaries Tim Chase <python.list@tim.thechases.com> - 2014-02-25 16:10 -0600
  Re: intersection, union, difference, symmetric difference for dictionaries mauro <mauro@gmail.com> - 2014-02-25 22:11 +0000
    Re: intersection, union, difference, symmetric difference for dictionaries Mark Lawrence <breamoreboy@yahoo.co.uk> - 2014-02-25 22:35 +0000
  Re: intersection, union, difference, symmetric difference for dictionaries MRAB <python@mrabarnett.plus.com> - 2014-02-25 23:07 +0000
    Re: intersection, union, difference, symmetric difference for dictionaries Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-02-26 00:37 +0000
  Re: intersection, union, difference, symmetric difference for dictionaries Ben Finney <ben+python@benfinney.id.au> - 2014-02-26 10:14 +1100
  Re: intersection, union, difference, symmetric difference for dictionaries MRAB <python@mrabarnett.plus.com> - 2014-02-25 23:25 +0000
  Re: intersection, union, difference, symmetric difference for dictionaries Grant Edwards <invalid@invalid.invalid> - 2014-02-25 20:44 +0000
  Re: intersection, union, difference, symmetric difference for dictionaries John Gordon <gordon@panix.com> - 2014-02-25 20:44 +0000
    Re: intersection, union, difference, symmetric difference for dictionaries Chris Angelico <rosuav@gmail.com> - 2014-03-02 09:29 +1100

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