Python identification dictionary

Question

Possible duplicate:
How to make a python dictionary that returns a key for keys that are not in the dictionary, instead of raising a KeyError?

I need something like defaultdict . However, for any key that is not in the dictionary, it must return the key itself.

What is the best way to do this?

Answer 1

Use the __missing__ magic method:

 >>> class KeyDict(dict): ... def __missing__(self, key): ... return key ... >>> x = KeyDict() >>> x[2] 2 >>> x[2]=0 >>> x[2] 0 >>> 

Answer 2

do you mean something like the following?

 value = dictionary.get(key, key) 

Answer 3

 class Dict(dict): def __getitem__(self, key): try: return super(Dict, self).__getitem__(key) except KeyError: return key >>> a = Dict() >>> a[1] 1 >>> a[1] = 'foo' >>> a[1] foo 

This works if you need to support Python <2.5 (which added the __missing__ method mentioned by @katrielalex).