min/max: "stable" invariant?

[Giovanni Bajo]

Hello,

assuming that a sequence contains multiple elements with minimum/maximum
value, do min/max guarantee to return the *first* element in the sequence
among those?

Example:
.... def __init__(self, x): self.x = x
....

L = [A(0), A(1), A(2), A(0)]
min(L, key=lambda a:a.x) is L[0] True
min(L, key=lambda a:a.x) is L[3]

False

Is this guaranteed by the Python language formal specification?
Is this guaranteed to always by true in CPython? (I guess so)

I can't find any mention in the documentation.

 

[Terry Reedy]

| Hello,
|
| assuming that a sequence contains multiple elements with minimum/maximum
| value, do min/max guarantee to return the *first* element in the sequence
| among those?
|
| Example:
|
| >>> class A:
| ... def __init__(self, x): self.x = x
| ...
| >>> L = [A(0), A(1), A(2), A(0)]
| >>> min(L, key=lambda a:a.x) is L[0]
| True
| >>> min(L, key=lambda a:a.x) is L[3]
| False
|
| Is this guaranteed by the Python language formal specification?
| Is this guaranteed to always by true in CPython? (I guess so)
|
| I can't find any mention in the documentation.

If there is no mention in the documentation (Lib Ref, Ch2 builtin
functions), then there is no guarantee.