Python dictionary: set value as the key string

Question

I have a python dictionary and want to set one of the values as the key itself whilst initializing the dict. That is:

dummy = dict(
  Key1 = ["SomeValue1", "Key1"],
  Key2 = ["SomeValue2", "Key2"],
  )

Can this be done programmably? That is, to skip writing the key again and set something like dummy.keys()[currentkeyindex] .

Answer 1

Using dict comprehension :

>>> values = [
...     ["SomeValue1", "Key1"],
...     ["SomeValue2", "Key2"],
... ]
>>> {x[1]: x for x in values}
{'Key2': ['SomeValue2', 'Key2'], 'Key1': ['SomeValue1', 'Key1']}

Answer 2

If you want to keep track of items as well then use defaultdict

>>> from collections import defaultdict                                                                                                      
>>> output = defaultdict(list)
>>> values = [
        ["SomeValue1", "Key1"],
        ["SomeValue2a", "Key2"],
        ["SomeValue2b", "Key2"]
    ]
>>> for x in values:
...     output[x[1]].append(x)
... 
>>> output
defaultdict(<type 'list'>, {
    'Key2': [['SomeValue2a', 'Key2'], ['SomeValue2b', 'Key2']], 
    'Key1': [['SomeValue1', 'Key1']]
})