About the implementation of del in Python 3

[Terry Reedy]

On 7/6/2017 11:41 AM, Marko Rauhamaa wrote:
> Chris Angelico <rosuav at gmail.com>:
> 
>> The formal definition is that objects have identities, and that
>> assignment (including function parameters and return values) gives you
>> a reference to the same object.
> 
> My example didn't contain a single assignment, but a variation of your
> statement would make a good part in a definition of identity.
> 
>> "A person just walked into the revolving door and came back out
>> again." "Is it the same person?" "I don't know. What's the definition
>> of identity?"
>>
>> Of course it's the same person. You don't need to identify that person
>> by a social security number in order to say "the SAME PERSON came back
>> out". You identify him/her by... identity.
> 
> Here's how identity is dealt with in First-Order Logic:
> 
>     <URL: https://en.wikipedia.org/wiki/First-order_logic#Semantics>
> 
> In other words, identity is mapped to the "sameness" in a domain of
> discourse.
> 
> In Second-Order Logic, you can define identity directly:
> 
>      ∀x ∀y x = y ↔ ∀P (P(x) ↔ P(y))
> 
> 
> Programming languages are different beasts, of course, but "objects" and
> "identity" are such important foundational topics that you'd expect a
> bit more than hand-waving when defining the data model.
> 
> As a good example of the style I'm looking for, take a look at:
> 
>     <URL: https://docs.oracle.com/javase/specs/jls/se7/html/jls-17.html>
> 
> 
> Marko
> 


-- 
Terry Jan Reedy