Python Dictionary return requested key if value does not exist

Question

I am looking for an easy way to be able to get a value from a dictionary, and if its not there, return the key that the user passed in.

E.g.:

>>> lookup = defaultdict(magic)
>>> print lookup['DNE']
'DNE'
>>> print lookup.get('DNE')
'DNE'
>>> print lookup['exists']
'some other value'
>>> print lookup.get('exists')
'some other value'

These will always be strings, but basically I am creating a language map and need an easy way to get a value, if it exists return it else return the key.

Is there any easy way to do this? Or should I just extend dict and do it manually.

Answer 1

I don't think defaultdict will help you here because the function that generates the default value does not have access to which key was requested.

However you use an ordinary dictionary and use get with a default value:

>>> lookup = {}
>>> key = 'DNE'
>>> lookup.get(key, key)
'DNE'

Answer 2

Should be possible with a lambda function

from collections import defaultdict
a = defaultdict((lambda : 'DNE'))

Edit: Sorry I misread the question. As the comment above already said. The way to go is extending the dict class.

>>> class mydict(dict):
...     def __missing__(self,key):
...         return key
... 
>>> a = mydict()
>>> a['asd']
'asd'