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'mapping' in weakrefs unneeded?

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(Repost from a mail I sent to python-devhttp://mail.python.org/pipermail/python-dev/2001-March/01which garnered no reponse.  Anyone here want to ignore it :)Hello all,  I'm starting to learn how to use weakrefs.  I'm curiousabout the function named 'mapping'.  It is implemented as:> def mapping(dict=None,weakkeys=0):>     if weakkeys:>         return WeakKeyDictionary(dict)>     else:>         return WeakValueDictionary(dict)Why is this a useful function?  Shouldn't people just callWeakKeyDictionary and WeakValueDictionary directly insteadof calling mapping with a parameter to specify which classto construct?If anything, this function is very confusing.  Take theassociated documentation as a case in point:> mapping([dict[, weakkeys=0]])> Return a weak dictionary. If dict is given and not None,> the new dictionary will contain the items contained in dict.> The values from dict must be weakly referencable; if any> values which would be inserted into the new mapping are not> weakly referencable, TypeError will be raised and the new> mapping will be empty.>> If the weakkeys argument is not given or zero, the values in> the dictionary are weak. That means the entries in the> dictionary will be discarded when no strong reference to the> value exists anymore.>> If the weakkeys argument is nonzero, the keys in the> dictionary are weak, i.e. the entry in the dictionary is> discarded when the last strong reference to the key is> discarded.As far as I can tell, this documentation is wrong, or atthe very least confusing.  For example, it says:> The values from dict must be weakly referencablebut when the weakkeys argument is nonzero,> the keys in the dictionary are weakSo must both keys and values be weak?  Or only the keys?I hope the latter since there are cases I can think ofwhere I want the keys to be weak and the values be types,hence non-weakreferencable.Wouldn't it be better to remove the 'mapping' function andonly have the WeakKeyDictionary and WeakValueDictionary.In which case the documentation becomes:> WeakValueDictionary([dict])> Return a weak dictionary. If dict is given and not None,> the new dictionary will contain the items contained in dict.> The values from dict must be weakly referencable; if any> values which would be inserted into the new mapping are not> weakly referencable, TypeError will be raised and the new> mapping will be empty.>> The values in> the dictionary are weak. That means the entries in the> dictionary will be discarded when no strong reference to the> value exists anymore.> WeakKeyDictionary([dict])> Return a weak dictionary. If dict is given and not None,> the new dictionary will contain the items contained in dict.> The keys from dict must be weakly referencable; if any> keys which would be inserted into the new mapping are not> weakly referencable, TypeError will be raised and the new> mapping will be empty.>> The keys in> the dictionary are weak. That means the entries in the> dictionary will be discarded when no strong reference to the> key exists anymore.Easier to read and to see the parallels between the twostyles, IMHO of course.[...python-dev specific paragraph omitted...]Sincerely,                    Andrewdalke at acm.org

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