[Python-ideas] Dict joining using + and +=
Guido van Rossum
guido at python.org
Mon Mar 4 14:24:39 EST 2019
* Dicts are not like sets because the ordering operators (<, <=, >, >=) are
not defined on dicts, but they implement subset comparisons for sets. I
think this is another argument pleading against | as the operator to
combine two dicts.
* Regarding how to construct the new set in __add__, I now think this
should be done like this:
def __add__(self, other):
<checks that other makes sense, else return NotImplemented>
new = self.copy() # A subclass may or may not choose to override
AFAICT this will give the expected result for defaultdict -- it keeps the
default factory from the left operand (i.e., self).
* Regarding how often this is needed, we know that this is proposed and
discussed at length every few years, so I think this will fill a real need.
* Regarding possible anti-patterns that this might encourage, I'm not aware
of problems around list + list, so this seems an unwarranted worry to me.
--Guido van Rossum (python.org/~guido)
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