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Date: Thu, 3 Oct 2013 14:14:27 +1000
Subject: Re: Tail recursion to while iteration in 2 easy steps
From: Chris Angelico <rosuav@gmail.com>
To: python-list@python.org
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Xref: csiph.com comp.lang.python:55403

On Thu, Oct 3, 2013 at 12:34 PM, Steven D'Aprano
<steve+comp.lang.python@pearwood.info> wrote:
> py> def f():
> ...     a = (1, 2, 3)
> ...     b = (1, 2, 3)
> ...     return a is b
> ...
> py> f()  # Are the tuples the same object?
> False

That just means the compiler doesn't detect reuse of the same tuple.
But compare:

>>> def f():
    return (1,2,3)

>>> f() is f()
True

Every time the function's called, it returns the same tuple (which
obviously can't be done with lists). And of course if that would be
dangerous, it's not done:

>>> def f():
    return (1,[2],3)

>>> f()[1].append("Hello")
>>> f()
(1, [2], 3)
>>> import dis
>>> dis.dis(f)
  2           0 LOAD_CONST               1 (1)
              3 LOAD_CONST               2 (2)
              6 BUILD_LIST               1
              9 LOAD_CONST               3 (3)
             12 BUILD_TUPLE              3
             15 RETURN_VALUE

ChrisA