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May 2011

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Re: [Python-ideas] [Python-Dev] What if replacing items in a dictionary returns the new dictionary?
by Roy Hyunjin Han 05 May '11

05 May '11

2011/5/5 Giuseppe Ottaviano <giuott(a)gmail.com>: >> The only thing I would add is obj.copy(), to ensure that the original >> dictionary is unchanged. >> >> class using(object): >> def __init__(self, obj): >> self._wrappee = obj.copy() > > My example was just a proof of concept, there are many other things > that may need to be taken care of (for example, non-callable > attributes). > BTW, the copy should be done outside. If the object is copied, I'd say > "using" is a poor choice of name for the proxy. You're right, I would need to do more work to get it to mimic the underlying object. I think I will stick with Oleg's suggestion to subclass dict for now; it's great for unit tests. Thanks for the idea, though. class ReplaceableDict(dict): def replace(self, **kwargs): 'Works for replacing string-based keys' return dict(self.items() + kwargs.items())

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Re: [Python-ideas] [Python-Dev] What if replacing items in a dictionary returns the new dictionary?
by Roy Hyunjin Han 05 May '11

05 May '11

>> 2011/4/29 Roy Hyunjin Han <starsareblueandfaraway(a)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(a)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.

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