Why does Python set([]) not equal {}?

Question

Set() and {} appear to give very similar behaviour, except for the confounding set([]) and {}. In the following comparisons, why is the last one False?

>>> set([1,2,3])=={1,2,3}
True
>>> set([1,2,3])==set([1,2,3])
True
>>> {1,2,3}=={1,2,3}
True
>>> set([])==set([])
True
>>> {}=={}
True
>>> set([])=={}
False

Because `{}` creates a dictionary! – MSeifert Jan 31 '17 at 14:39 — MSeifert, Jan 31 '17 at 14:39
because `type({})` is `dict`. – Willem Van Onsem Jan 31 '17 at 14:40 — Willem Van Onsem, Jan 31 '17 at 14:40

score 7 · Accepted Answer · answered Jan 31 '17 at 14:39

7

Because the {} literal is reserved for the empty dict, not the empty set

answered Jan 31 '17 at 14:39

blue_note

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score 2 · Answer 2 · answered Jan 31 '17 at 14:40

2

Because {} creates a dict.

In[49]: type({})
Out[49]: dict

answered Jan 31 '17 at 14:40

miradulo

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score 0 · Answer 3 · answered Jan 31 '17 at 14:41

To create an empty set, you can only use set().

Sets are collections of unique elements and you cannot order them. Lists are ordered sequences of elements, and values can be repeated. Dictionaries map keys to values, keys must be unique. Set and dictionary keys must meet other restrictions as well, so that Python can actually keep track of them efficiently and know they are and will remain unique.

Why does Python set([]) not equal {}?

3 Answers3