[Python-Dev] Proper tail recursion

Michael Hudson mwh at python.net
Thu Jul 15 11:19:04 CEST 2004

Christopher T King <squirrel at WPI.EDU> writes:

> On Wed, 14 Jul 2004, Michael Hudson wrote:
>> I guess I could have said this in c.l.py, but: what's the point?  I
>> don't think I've ever had a situation where hitting the recursion
>> limit wasn't a bug, and given a) the ease with which a non-contrivedly
>> tail recursive algorithm can usually be rewritten iteratively and b)
>> the (lack of) speed of function calls in today's Python I can't see
>> any huge real advantage to this patch.
> To tell the truth, I don't really have any immediate use for this
> functionality, either, but since it turned out to be so easy to implement,
> I ask, "why not?" ;) Presuming it doesn't break any existing
> functionality, of course.* I prefer to think of it in the same light as
> the opcode prediction macros, i.e. as a performance enhancement, rather
> than as an attempt to introduce a new paradigm to the language (which it
> isn't).

*Is* it actually a performance enhancement?

> * I know it breaks stack traces, but the final implementation will only be 
> used when the -O flag is specified, or some other such indicator is set.

It doesn't seem to me that it necessarily has to break
tracebacks...  Haven't looked at the patch, though.  I guess there's a
fair chance that any performance enhancements it acheives are from
resuing frame objects (if that's what it does) though.


  I've even been known to get Marmite *near* my mouth -- but never
  actually in it yet.  Vegamite is right out.
 UnicodeError: ASCII unpalatable error: vegamite found, ham expected
                                       -- Tim Peters, comp.lang.python

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