I have a dictionary of lists, and it should be initialized with default keys. I guess, the code below is not good (I mean, it works, but I don't feel that it is written in the pythonic way):
d = {'a' : [], 'b' : [], 'c' : []}
So I want to use something more pythonic like defaultict:
d = defaultdict(list)
However, every tutorial that I've seen dynamically sets the new keys. But in my case all the keys should be defined from the start. I'm parsing other data structures, and I add values to my dictionary only if specific key in the structure also contains in my dictionary.
How can I set the default keys?
From the comments, I'm assuming you want a dictionary that fits the following conditions:
@Aaron_lab has the right method, but there's a slightly cleaner way:
d = defaultdict(list,{ k:[] for k in ('a','b','c') })
That's already reasonable but you can shorten that up a bit with a dict comprehension that uses a standard list of keys.
>>> standard_keys = ['a', 'b', 'c']
>>> d1 = {key:[] for key in standard_keys}
>>> d2 = {key:[] for key in standard_keys}
>>> ...
If you're going to pre-initialize to empty lists, there is no need for a defaultdict. Simple dict-comprehension gets the job done clearly and cleanly:
>>> {k : [] for k in ['a', 'b', 'c']}
{'a': [], 'b': [], 'c': []}