Postfix/Prefix Operators (++,--)

Joshua Marshall joshway_without_spam at myway.com
Fri Jun 6 19:57:32 CEST 2003


Peter Hansen <peter at engcorp.com> wrote:
> Joshua Marshall wrote:
...
>> I wouldn't design ++ to error in this case:
>> 
>>   >>> c = 1
>>   >>> a = c++
>>   >>> a
>>   1
>>   >>> c
>>   2

> Except that that violates a fundamental aspect of Python, which while
> I can't describe it in the best technical terms as I don't ever work 
> at the compiler level, could be said as "you are rebinding a name (c)
> without using an assignment statement".

Agreed.  One reason I'm against this feature going into Python is that
I think the ability to rebind variables in expressions is a bad idea.

> I'm not sure whether there is ever a case where this is true in
> regular Python, and I suspect that if you were to attempt to
> implement this, it would require fundamental changes that would make
> Python not Python...  so I'm still confident there's "no chance of
> having it, and no reason to have it."

List comprehensions let you rebind a variable in an expression, so
there is some precedent for this:

  >>> c = 1
  >>> a = [c - 1 for c in [c + 1]][0]
  >>> a
  1
  >>> c
  2

but I'm not fond of list comprehensions either.




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