Re: [Python-ideas] Adding "+" and "+=" operators to dict

Feb. 14, 2015

...
On Feb 14, 2015, at 1:09 AM, Stephen J. Turnbull <stephen@xemacs.org> wrote:
Chris Barker writes:
...
merging two dicts certainly is _something_ like addition.
But you can't say what that something is with precision, even if you
abstract, and nobody contests that different applications of dicts
have naively *different*, and in implementation incompatible,
"somethings".
So AFAICS you have to fall back on "my editor forces me to type all
the characters, so let's choose the interpretation I use most often
so cI can save some typing without suffering too much cognitive
dissonance.”
Or we can choose the interpretation that has already been chosen by
multiple locations within Python. That keys are replaced and rhs
wins. This is consistent with basically every location in the stdlib
and Python core where two dicts get combined in some fashion other than
specialized subclasses.

    >>> a = {1: True, 2: True}
    >>> b = {2: False, 3: False}
    >>> dict(list(a.items()) + list(b.items()))
    {1: True, 2: False, 3: False}

    And

    >>> a = {1: True, 2: True}
    >>> b = {2: False, 3: False}
    >>> c = a.copy()
    >>> c.update(b)
    >>> c
    {1: True, 2: False, 3: False}

    And

    >>> {1: True, 2: True, 2: False, 3: False}
    >>> {1: True, 2: False, 3: False}

    And

    >>> a = {"a": True, "b": True}
    >>> b = {"b": False, "c": False}
    >>> dict(a, **b)
    {'b': False, 'c': False, 'a': True}

---
Donald Stufft
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