[issue38853] set.repr breaches docstring contract
New submission from Cat Chenal :
S = {19,8,-1,25,0,1,2,3,4,5,6,7}
print('Set S = {{19,8,-1,25,0,1,2,3,4,5,6,7}}')
The set is represented by a new string-ordered set:
print(f'Its repr is:\n{S}\n')
Output:
{0, 1, 2, 3, 4, 5, 6, 7, 8, 19, 25, -1}
This is a breach of the contract stated in the docstring: "Build an unordered
collection of unique elements."
--
components: ctypes
messages: 356991
nosy: Ylem
priority: normal
severity: normal
status: open
title: set.repr breaches docstring contract
type: behavior
versions: Python 3.6
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[issue38855] test_unpack.py does not catch the unpacking of a set
New submission from Cat Chenal :
S = {19,8,-1,25,0,1,2,3,4,5,6,7}
a, *b, c = S
print('a:', a)
print('b:', b)
print('c:', c)
Output:
a: 0
b: [1, 2, 3, 4, 5, 6, 7, 8, 19, 25]
c: -1
Either test_unpack.py needs a test for "non-indexable object" to prevent this
unpacking of a non-sequence, or the unpacking of a set should be implemented
(granted the ordered repr of a set is changed to unordered, see Issue38853).
Being able to "unpack" a set would be nice to have, imho, because one would use
that operation to obtain a partition (over unordered elements).
--
components: Tests, ctypes
messages: 356994
nosy: Ylem
priority: normal
severity: normal
status: open
title: test_unpack.py does not catch the unpacking of a set
versions: Python 3.6
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[issue38853] set.repr breaches docstring contract
Cat Chenal added the comment:
Thank you for pointing out my lack of clarity: I apologize.
I probably should not have split this issue in two (issue38855).
My confusion stems from the fact that I expected the unpacking of a set to
return the same output as that obtained from the unpacking of a list.
>From my testing, I gather that the unpacking of a set is performed via its
>repr, which uses "some ordering".
In closing, I want to note two points:
1. repr is apparently platform-dependent (here: Python 3.6.7 [MSC v.1900 64 bit
(AMD64)]):
The code given by steven.daprano run in a jupyter lab cell or in VS Code yields
a different output:
>>> repr({4, 5, 2**31+1, 2, 2**31+2, 3, 2**31, 0})
'{2147483648, 2147483649, 2, 2147483650, 4, 5, 3, 0}'
2. Testing reviewer's assertion: "The specific order you see will depend on the
specific values in the set, as well as the order that they were inserted,
deleted, and/or re-inserted in some arbitrary way."
This counter example, where element 0 is moved to the second position, shows
that there is not such order dependence:
>>> repr({4, 0, 5, 2**31+1, 2, 2**31+2, 3, 2**31})
'{0, 2147483649, 2, 2147483650, 4, 5, 3, 2147483648}'
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