Perl and Python, a practical side-by-side example.

[Ben Finney]

Bjoern Schliessmann <usenet-mail-0306.20.chr0n0ss at spamgourmet.com> writes:

> Bruno Desthuilliers wrote:
> > Shawn Milo a écrit :
>
> >>     if recs.has_key(piid) is False:
> > 
> > 'is' is the identity operator - practically, in CPython, it
> > compares memory addresses. You *dont* want to use it here.
>
> It's recommended to use "is None"; why not "is False"? Are there
> multiple False instances or is False generated somehow?

I'd recommend against using "is False" simply because it's more
confusing. This is better::

    if not recs.has_key(piid):      # [1]

Moreover, any 'if' statement expects a boolean expression *anyway*, so
there's no point testing for identity against False. Otherwise, the
following would be just as reasonable::

    if (recs.has_key(piid) is False) is True:

Or perhaps:

    if (((((recs.has_key(piid) is False) is True) is False) is False) is True):


[1]: yes, this is even better written as 'if not piid in recs', but
that's beside the point for this discussion.

-- 
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Ben Finney