Is Python's bool sorting defined?

Question

Is the ordering of True and False well defined in Python, or is it left as an implementation detail?

From the console, I'm seeing False sort before True...but I don't know if that's a behavior I should rely on or not.

(I'm sure there's some Python doc about this, but I can't find it...)

For bonus points, try doing arithmetic with bools. `(True + True) ** -True == 0.5`... — Jamey Sharp, Nov 13 '12 at 00:14
@rsegal I discovered that `sum([True, False, ...])` is a nice way to count the number of true cases in a list, and the above awful abuse followed quickly after. — Jamey Sharp, Nov 13 '12 at 00:27
@JameySharp that's actually not a terrible idea. It's almost like a `reduce(filter(list))`. Hmmmm. — rsegal, Nov 13 '12 at 00:29
@JameySharp `sum(1 for element in iterable if element)` should be well-defined. — Blacklight Shining, Feb 10 '14 at 12:01

score 25 · Accepted Answer · answered Nov 13 '12 at 00:21

25

http://docs.python.org/2/reference/datamodel.html#the-standard-type-hierarchy

Booleans: These represent the truth values False and True. The two objects representing the values False and True are the only Boolean objects. The Boolean type is a subtype of plain integers, and Boolean values behave like the values 0 and 1, respectively, in almost all contexts, the exception being that when converted to a string, the strings "False" or "True" are returned, respectively.

This reads to me that the python language requires False < True, False == 0, True == 1, True != 2.

The same wording is retained in Python 3 as well.

answered Nov 13 '12 at 00:21

Bill Lynch

80,138
16
128
173

2

If you're unsure you agree with sharth's understanding, try plugging it into an interpreter. You'll quickly verify that `False < True`. In fact, reading the spec and playing around with it into the interpreter are always good ideas! – rsegal Nov 13 '12 at 00:27
It's worth noting that 'sorting is defined' basically means comparisons are defined, which means that if something is less than something else, it will be sorted correctly and as noted here `False < True`. – Grismar Dec 02 '19 at 00:08

score 1 · Answer 2 · answered Dec 02 '19 at 00:01

1

We can show bool is sortable using the Python REPL, with False being the lower value:

>>> sorted([False, True, True, False, True])
[False, False, True, True, True]

answered Dec 02 '19 at 00:01

Graham Lea

5,797
3
40
55

Is Python's bool sorting defined?

2 Answers2