subscripting Python 3 dicts/getting the only value in a Python 3 dict

[Steven D'Aprano]

On Wed, 13 Jan 2016 03:50 am, Nick Mellor wrote:

> Hi all,
> 
> Seemingly simple problem:
> 
> There is a case in my code where I know a dictionary has only one item in
> it. I want to get the value of that item, whatever the key is.

[snip examples]

> None of this feels like the "one, and preferably only one, obvious way to
> do it" we all strive for. Any other ideas?

That's because this is a somewhat weird case. A dict with only one item that
you don't know the key of? Who does that? (Well, apart from you,
obviously.)

Three solutions:


item = d.popitem()[1]  # But this modifies the dict.

# Use tuple rather than list for efficiency.
item = tuple(d.values())[0]


Probably the best solution, because it will conveniently raise an exception
if your assumption that the dict has exactly one item is wrong:

item, = d.values()  # Note the comma after "item".


The comma turns the assignment into sequence unpacking. Normally we would
write something like this:

a, b, c, d = four_items

but you can unpack a sequence of one item too. If you really want to make it
obvious that the comma isn't a typo:

(item,) = d.values()




-- 
Steven