missing? dictionary methods

[Ron]

On 21 Mar 2005 08:21:40 GMT, Antoon Pardon <apardon at forel.vub.ac.be>
wrote:

>Well at least I find them missing.
>
>For the moment I frequently come across the following cases.
>
>1) Two files, each with key-value pairs for the same dictionary.
>However it is an error if the second file contains a key that
>was not in the first file.
>
>In treating the second file I miss a 'set' method.
>dct.set(key, value) would be equivallent to dct[key] = value,
>except that it would raise a KeyError if the key wasn't
>already in the dictionary.
>
>
>2) One file with key-value pairs. However it is an error
>if a key is duplicated in the file.
>
>In treating such files I miss a 'make' method.
>dct.make(key, value) would be equivallent to dct[key] = value.
>except that it would raise a KeyError if the key was
>already in the dictionary.
>
>
>What do other people think about this?


There is a has_key(k) method that helps with these.

Adding these wouldn't be that hard and it can apply to all
dictionaries with any data.  

class newdict(dict):    
    def new_key( self, key, value):
        if self.has_key(key):
            raise KeyError, 'key already exists'
        else:
            self[key]=value            
    def set_key( self, key, value):
        if self.has_key(key):
            self[key]=value
        else:
            raise KeyError, 'key does not exist'

d = newdict()
for x in list('abc'):
    d[x]=x
print d
d.new_key('z', 'z')
d.set_key('a', 'b')
print d

Which is faster?  (has_key()) or (key in keys())?