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

[Donald Stufft]

> On Feb 11, 2015, at 2:21 AM, Ian Lee <ianlee1521 at gmail.com> wrote:
> 
> I mentioned this on the python-dev list [1] originally as a +1 to someone else suggesting the idea [2]. It also came up in a response to my post that I can't seem to find in the archives, so I've quoted it below [3].
> 
> As the subject says, the idea would be to add a "+" and "+=" operator to dict that would provide the following behavior:
> 
> >>> {'x': 1, 'y': 2} + {'z': 3}
> {'x': 1, 'y': 2, 'z': 3}
> 
> With the only potentially non obvious case I can see then is when there are duplicate keys, in which case the syntax could just be defined that last setter wins, e.g.:
> 
> >>> {'x': 1, 'y': 2} + {'x': 3}
> {'x': 3, 'y': 2}
> 
> Which is analogous to the example:
> 
> >>> new_dict = dict1.copy()
> >>> new_dict.update(dict2)
> 
> With "+=" then essentially ending up being an alias for ``dict.update(...)``.
> 
> I'd be happy to champion this as a PEP if the feedback / public opinion heads in that direction. 
> 
> 
> [1] https://mail.python.org/pipermail/python-dev/2015-February/138150.html <https://mail.python.org/pipermail/python-dev/2015-February/138150.html>
> [2] https://mail.python.org/pipermail/python-dev/2015-February/138116.html <https://mail.python.org/pipermail/python-dev/2015-February/138116.html>
> [3] John Wong -- 
> Well looking at just list
> a + b yields new list
> a += b yields modified a
> then there is also .extend in list. etc.  
> so do we want to follow list's footstep? I like + because + is more natural to read. Maybe this needs to be a separate thread. I am actually amazed to remember dict + dict is not possible... there must be a reason (performance??) for this...
> 

I’d really like this change and I think that it makes sense. The only thing I’d change is that I think the | operator makes more sense than +. dicts are more like sets than they are like lists so a union operator makes more sense I think.

---
Donald Stufft
PGP: 7C6B 7C5D 5E2B 6356 A926 F04F 6E3C BCE9 3372 DCFA

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