[melbourne-pug] Why can't two dicts be added together?

[Brett Wilkins]

In Ruby there is the merge method (returns a new hash) and the merge! method (modifies the hash that the method is called from). These methods are documented as preferring the values on the passed-in in the case of key collision. ActiveSupport (part of the Ruby on Rails ecosystem) provides reverse_merge and reverse_merge!, which prefer the acting hash's values over the values of the hash that is passed in.

-- 
Brett Wilkins

On 17 October 2013 at 11:58:46 AM, Javier Candeira (javier at candeira.com) wrote:

Python culture runs counter to monkeypatching standard library  
objects, but this looks be easy to do via injecting __add__ (and  
__iadd__ for "d1 += d2") straight into the dict class. In Ruby it's  
done In fact it looks so obvious that ...  

/me googles...  

https://www.google.com.au/search?q=dict+__add__  

The first result is a bug report, but it was rejected before it got to  
PEP stage even: http://bugs.python.org/issue6410. Contains good  
rationale for the rejection.  

J  

On Thu, Oct 17, 2013 at 11:31 AM, Sam Lai <samuel.lai at gmail.com> wrote:  
> It's almost Friday, so I have a question where I'm pretty sure I'm  
> missing something obvious.  
>  
> Given,  
>  
> d1 = { 'a' : 'b' }  
> d2 = { 'c' : 'd' }  
>  
> ... why isn't d3 = d1 + d2 implemented to be equivalent to -  
>  
> d3 = { }  
> d3.update(d1)  
> d3.update(d2)  
>  
> It doesn't work for sets either, but it works in this fashion for  
> lists. Is this because the operation is non-commutative for sets and  
> dicts and may result in a loss of data when clashing keys are  
> involved? Isn't that implicit when working with sets and dicts?  
>  
> Sam  
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