Passing a callable object to Thread

Paul Rubin http
Tue Feb 19 01:00:43 CET 2008


Jeff Schwab <jeff at schwabcenter.com> writes:
> >> In CS, a tuple is a kind of data structure that is specifically not
> >> identical with any of its elements.  That's the sort of tuple used in
> >> Python.

The usual CS meaning of "tuple" is more like the physics meaning than
like the Python meaning, I think.  

> >>>> (a,) is (a,)
> > False
> 
> The tuple on the left is not identical with the tuple on the right,
> even though they are equivalent.

Implementation artifact.  It could be constant folded.
   x = (a,)
   y = x
   x is y
should print True.

> An interesting thing about Python is that numbers of built-in types
> are flyweights.  Unlike literals of non-flyweight types, distinct
> instances of a given numeric literal actually refer to the same object:
> 
>  >>> 5 is 5
> True
>  >>> 999999999999999999999999999999 is 999999999999999999999999999999
> True
>  >>> 3.5 is 3.5
> True

Again an implementation artifact, not guaranteed by the language.  Try:
  (5+1) is (5+1)
then try
  (999999999999999999999999999999+1) is (999999999999999999999999999999+1)



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