Dict to tuple : why does it not take all values?

Question

I converted a dictionary to tuple so it can be hashable.

DATA_ILLUMINANTS = {
'LED': tuple({
    380.0: 0.006,
    385.0: 0.013,
    ...
    780.0: 0.108,})
    }

When I print the tuple, there is not the second column of data, it is :

(380.0, 385.0, 390.0, 395.0, 400.0, ... , 780.0)

Any idea why ?

I use the 'LED' tuple in another code that return me the following error : AttributeError: 'tuple' object has no attribute 'shape' and I suppose this is because data are missing in the tuple.

When you iterate over a dictionary, you iterate over its _keys_. What output were you expecting - `tuple({...}.items())`, maybe? — jonrsharpe, Apr 30 '21 at 07:54
The "tuple object has no attribute 'shape'" error is symptomatic of that code needing a Numpy array, but that's another can of worms. — AKX, Apr 30 '21 at 07:56
Dict values don't have to be hashable. Only the keys do. You could use the dict as is; no need to convert it to a tuple. — John Kugelman, Apr 30 '21 at 07:57
If you're converting a dict literal to a tuple, as in your example, why not simply use a tuple literal in the first place? — Roel Schroeven, Apr 30 '21 at 08:47

score 2 · Accepted Answer · answered Apr 30 '21 at 07:54

2

Iterating over a dict (which is what e.g. tuple() does) iterates over the keys.

You'll want tuple({...}.items()) to get a tuple of 2-tuples.

>>> x = {1: 2, 3: 4, 5: 6}
>>> tuple(x)
(1, 3, 5)
>>> tuple(x.items())
((1, 2), (3, 4), (5, 6))
>>>

answered Apr 30 '21 at 07:54

AKX

152,115
15
115
172

2

Iteration order may be unpredictable. It would be wise to sort the items, too. – John Kugelman Apr 30 '21 at 07:56
@JohnKugelman That depends on the version of CPython in use and OP's use case, but yep :) – AKX Apr 30 '21 at 07:57
@JohnKugelman effectively since CPython 3.6, and since Python 3.7+ officially, `dict` objects maintain insertion order. – juanpa.arrivillaga Apr 30 '21 at 08:00
1

Right, this is why I hedged with "may be". For clarity's sake, I recommend sorting. – John Kugelman Apr 30 '21 at 08:01

score 1 · Answer 2 · answered Apr 30 '21 at 07:55

1

tuple() will iterate through the given object, here a dict. The dict iterate over the keys, this is why. You can force it to iterate over the items: tuple({ 380.0: 0.006, 385.0: 0.013, ... 780.0: 0.108,}.items() )

answered Apr 30 '21 at 07:55

pygame

121
5

Dict to tuple : why does it not take all values?

2 Answers2