It feels so good, so quick and not C!

Steven Taschuk staschuk at
Wed Mar 19 06:19:08 CET 2003

Quoth John Machin:
> Steven Taschuk <staschuk at> wrote in message news:<mailman.1047969613.29891.python-list at>...
  [...a strrev implementation...]
> > If you're just learning Python, you might want to spend a few
> > minutes studying this version.  It has one slightly subtle point
> > for which I would write a comment if this were real code.)
> Which if any of the following "subtle" points did you mean? (1)
> "backwards" is as twice as large as it needs to be, with the unwanted
> guff jettisoned by zip().  [...]

That's the one, more or less.

Imho exploiting this behaviour of zip deserves the word subtle,
without scare quotes, for a Python newcomer.  The point, of
course, is that the backwards range can be written more clearly
this way.

> [...] (2) "forwards", "backwards", and the zip()
> result constitute about (3 * len(orig)) objects clogging up memory.

*shrug*  So use xrange and izip.

> (3) The cuteness of swapping by "x, y = y, x" hides the overhead of
> packing and unpacking a 2-tuple, which may or may not be faster than
> the traditional 3-assignment method.

I confess a weakness for the cute swapping method; on my machine
it is, in fact, perhaps 5% slower.  I don't usually worry about it.

Steven Taschuk                                     staschuk at
Receive them ignorant; dispatch them confused.  (Weschler's Teaching Motto)

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