Why does Python produce different sets from identical input?

Question

Condider the following example:

>>> {1, True}
set([True])
>>
>>> {True, 1}
set([1])

Why is the set represented differently, depending on the order of the elements?

Because booleans are a subclass of `int` and `True == 1` (and `False == 0`). This is a duplicate. — Martijn Pieters, Dec 24 '13 at 09:24
Related: [Is False == 0 and True == 1 in Python an implementation detail or is it guaranteed by the language?](http://stackoverflow.com/q/2764017) Hard to searh for the duplicate. — Martijn Pieters, Dec 24 '13 at 09:35
@MartijnPieters One of the examples can be found [here](http://stackoverflow.com/questions/10419918/adding-the-number-1-to-a-set-has-no-effect/). — devnull, Dec 24 '13 at 09:38

score 4 · Accepted Answer · answered Dec 24 '13 at 09:24

4

This happens because 1 and True are equal to each other:

>>> True == 1
True
>>> 1 == True
True

The set retains one element from each equality class.

answered Dec 24 '13 at 09:24

NPE

score 0 · Answer 2 · answered Dec 24 '13 at 09:37

0

bool is subclass of int class

>>> issubclass(bool, int)
True

>>> True+1
2
>>> True == 1
True

answered Dec 24 '13 at 09:37

Vb407

2 Answers2