[Python-ideas] Fwd: Boolean behavior of None

Thu Jan 17 15:54:28 CET 2013

On 1/17/2013 8:10 AM, Ilkka Pelkonen wrote:
> Hi Oleg, others,
> It's not that it can't be done, just that it does something you don't 
> expect. I've been professionally working with C++ for nine years in 
> large-scale Windows systems, and I do expect a boolean expression 
> return a boolean value.
>> Or, can you show me an example how the developer would benefit of the 
> current behavior? Any operator traditionally considered as boolean 
> will do.
>> Regards,
> Ilkka

Ilkka, welcome to the Python community. Python is a wonderfully 
expressive language once you learn its subtleties.
Python and C++ are different. If they weren't, we'd only have one 
language, not two. The short-circuiting operations "and" and "or" 
behave as they do for a reason. As an example, a common way to deal 
with default values:
 def accumulate(value, to=None):
 to = to or []
 to.append(value)
 # Forget whether this is a good function or not..
 return to
If "or" always returned a boolean, as I'm assuming you'd prefer, then 
we'd have a much clumsier time defaulting values like this.
--Ned.
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