[Python-Dev] What if replacing items in a dictionary returns the new dictionary?

[Roy Hyunjin Han]

>> 2011/4/29 Roy Hyunjin Han <starsareblueandfaraway at gmail.com>:
>> It would be convenient if replacing items in a dictionary returns the
>> new dictionary, in a manner analogous to str.replace().  What do you
>> think?
>>
>>    # Current behavior
>>    x = {'key1': 1}
>>    x.update(key1=3) == None
>>    x == {'key1': 3} # Original variable has changed
>>
>>    # Possible behavior
>>    x = {'key1': 1}
>>    x.replace(key1=3) == {'key1': 3}
>>    x == {'key1': 1} # Original variable is unchanged
>>
> 2011/5/5 Giuseppe Ottaviano <giuott at gmail.com>:
> In general nothing stops you to use a proxy object that returns itself
> after each method call, something like
>
> class using(object):
>    def __init__(self, obj):
>        self._wrappee = obj
>
>    def unwrap(self):
>        return self._wrappee
>
>    def __getattr__(self, attr):
>        def wrapper(*args, **kwargs):
>            getattr(self._wrappee, attr)(*args, **kwargs)
>            return self
>        return wrapper
>
>
> d = dict()
> print using(d).update(dict(a=1)).update(dict(b=2)).unwrap()
> # prints {'a': 1, 'b': 2}
> l = list()
> print using(l).append(1).append(2).unwrap()
> # prints [1, 2]

Cool!  I never thought of that.  That's a great snippet.

I'll forward this to the python-ideas list.  I don't think the
python-dev people want this discussion to continue on their mailing
list.