Joe Strout wrote: > First, I want to thank everyone for your patience -- I think we're > making progress towards a consensus. > Phew. > >> But putting that aside, consider the Python >> code "x = 1". Which statement would you agree with? >> >> (A) The value of x is 1. > > Only speaking loosely (which we can get away with because numbers are > immutable types, as pointed out in the last section of [1]). > I'd agree this is a valid way to describe the post-condition of the assignment.
>> (B) The value of x is an implementation-specific thing which is >> determined at runtime. At the level of the Python virtual machine, the >> value of x is arbitrary and can't be determined. > > Hmm, this might be true to somebody working at the implementation level, > but I think we're all agreed that that's not the level of this > discussion. What's relevant here is how the language actually behaves, > as observable by tests written in that language. > I'd actually say "x contains a reference to 1", claim that was equivalent to (A) above and cite Humpty Dumpty as my justification [1]. >> If you answer (A), then your claim that Python is call-by-value is false. > > Correct. > >> If you answer (B), then your claim that Python is call-by-value is true >> but pointless, obtuse and obfuscatory. > > Correct again. My answer is: > > (C) The value of x is a reference to an immutable object with the value > of 1. (That's too wordy for casual conversation so we might casually > reduce this to (A), as long as we all understand that (A) is not > actually true. It's a harmless fiction as long as the object is > immutable; it becomes important when we're dealing with mutable objects.) > I am unsure here as to why you find it necessary to refer to 1's immutability. How does this alter the essence of the situation? [...] > > Not that I'm trying to argue from authority; I'm trying to argue from > logic. I suspect, though, that your last comment gets to the crux of > the matter, and reinforces my guess above: you don't think c-b-v means > what most people think it means. Indeed, you don't think any of the > languages shown at [1] are, in fact, c-b-v languages. If so, then we > should focus on that and see if we can find a definitive answer. > You're right. Observable progress, I think. regards Steve [1] http://www.sundials.org/about/humpty.htm -- Steve Holden +1 571 484 6266 +1 800 494 3119 Holden Web LLC http://www.holdenweb.com/ -- http://mail.python.org/mailman/listinfo/python-list
