What will be the time complexity of list(dict.keys()) in python3

Question

I was solving an algorithm question using list(dict.keys()) it was taking a lot more time than OrderedDict dict.popitem(0) I know it'll return generator type object we can traverse over it and get every element like range in list.

Answer 1

Time complexity is O(n) as you create a new list made of all elements.

If you just want the first, I suggest you to next(iter(dict)) or next(iter(dict.items())) which will bring you the first key or (key, value) pair respectively at O(1) .

You can catch StopIteration to make sure the dict isn't empty or return a default value from next() :

>>> def take_first(d):
...   return next(iter(d), None)
...
>>> take_first({"a": 1, "b": 2})
'a'
>>> take_first({})
>>> # (None)