[Python-Dev] RFC: PEP 509: Add a private version to dict (original) (raw)

Oscar Benjamin oscar.j.benjamin at gmail.com
Fri Apr 15 16:33:44 EDT 2016

On 15 April 2016 at 18:54, Jim J. Jewett <jimjjewett at gmail.com> wrote:

[2A] Do you want to promise that replacing a value with a non-identical object will trigger a versiontag update even if the objects are equal? I would vote no, but I realize backwards-compatibility may create such a promise implicitly.

It needs to trigger a version update. Equality doesn't guarantee any kind of equivalence in Python. It's not even guaranteed that a==b will come to the same value if evaluated twice in a row.

An example:

from fractions import Fraction as F F(1) == 1 True d = globals() d['a'] = F(1) a.limitdenominator() Fraction(1, 1) d['a'] = 1 a.limitdenominator() Traceback (most recent call last): File "", line 1, in AttributeError: 'int' object has no attribute 'limit_denominator'

-- Oscar

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