Suggestions for good programming practices?

[Bengt Richter]

On 24 Jun 2002 23:16:02 -0400, aahz at pythoncraft.com (Aahz) wrote:

>In article <mailman.1024951532.5616.python-list at python.org>,
>David LeBlanc <whisper at oz.net> wrote:
>>Mark:
>>>
>>> When evaluating whether a variable is None, don't compare it like this:
>>>
>>> 	if x == None:
>>>
>>> instead, use:
>>>
>>> 	if x:
>>>
>>> or:
>>>
>>> 	if not x:
>>>
>>> The encourages a polymorphic approach.  If you must compare to
>>> None, use the identify operator rather than equality:
>>>
>>> 	if x is None:
>>>
>>> or:
>>>
>>> 	if x is not None:
>>
>>I'm curious to know how this encourages polymorphism, and how making a
>>conditional test implicit rather then explicit is good practice?
>
>Depends on what you're testing for.  One of the big features of Python's
>object model is that any "empty" object tests as false: None, 0, "", (),
>[], and {}.  Testing for a specific false value (such as 0 or None)
>prevents you from easily changing the object being used.  Rely on the
>object to tell you whether it's true or false, and you'll be fine.
>
>That's polymorphic.

This kind of usage seems common:

 >>> def foo(x=None):
 ...     if x: print "Aahz says we'll be fine with %s" % `x`
 ...     else: print "But what about %s ?" % `x`
 ...     if x is None: print "Here we know we were passed %s (maybe by default)" % `x`
 ...
 >>> foo('something')
 Aahz says we'll be fine with 'something'
 >>> foo(0)
 But what about 0 ?
 >>> foo()
 But what about None ?
 Here we know we were passed None (maybe by default)

Do you recommend using def foo(*args) and testing len(args) instead?

Regards,
Bengt Richter