Pragmatics of the standard is() function

[Den]

On Nov 26, 3:01 pm, Steven D'Aprano <steve
+comp.lang.pyt... at pearwood.info> wrote:
> On Sat, 26 Nov 2011 22:20:36 +0100, candide wrote:
>>SNIP<<
>
> That is correct. You probably should rarely use `is`. Apart from testing
> for None, use of `is` should be rare.
>
> --
> Steven

With respect, I disagree with advice that the use of a language
construct should be rare.  All constructs should be used
*appropriately*.

While in general a particular use of a Python construct may be rare,
if the programmer is involved deeply with that rare use, then it is
NOT rare to him/her.  Thus, for a particular programmer, use of 'is'
may be quite frequent because the program they're working on requires
knowledge of object identity.

The same goes for global variables, by the way.  While it's easy to
shoot yourself in the foot with global variables, that doesn't lead to
never-use-them.  It leads to use-them-appropriately-and-carefully.

Sorry, you plucked a string of mine.  One does not throw a tool out of
your tool box because it might be dangerous.  Table saws are
incredibly dangerous, but in the hands of a skilled operator can be
competently and safely used to produce beautiful woodwork.  To say
*never* use a table saw because it's dangerous is silly.

Language constructs are put there intentionally.  Advice that they be
used *rarely* or *never* should *never* be given ((chuckle)).  Just
learn what they are, learn how they work, learn what the consequences
of misuse can be (loss of a hand, in the case of a table saw), and use
them confidently when the circumstances make them the best choice of
tool to solve your problem.

To make a long comment short (too late!!) learn the differences
between 'is' and ==, and use them appropriately.  When I was learning
Python, I found the two books by Mark Lutz to be filled with
information of such things as these.

D