[Python-Dev] Default constructor values (Re: [Python-checkins] python/dist/src/Doc/lib libfuncs.tex,1.134,1.135)

[M.-A. Lemburg]

Guido van Rossum wrote:
>>>- bool() called without arguments now returns False rather than
>>>  raising an exception.  This is consistent with calling the
>>>  constructors for the other builtin types -- called without argument
>>>  they all return the false value of that type.  (SF patch #724135)
>>
>>I seriously question the usefulness of such an approach. It
>>doesn't seem to buy us anything and is likely to hide typos
>>or progamming errors.
> 
> Types with constructors that insist on an argument are problematic to
> generic code that tries to instantiate a type by simply calling it.

The types we are talking about all define values -- why would you
want to create an object without even knowing the value they
represent ? Can you give an example ?

BTW, your "simply calling the constructor" is a rather dangerous way
of doing inspection: how can you be sure that the constructor
has no side-effects ?

> I don't think that there's much chance that e.g. str() or int() will
> be used by accident and not discovered right away.

How's that ? Since it is perfectly valid to write str() and int()
without arguments, not even the editor can help notice these
cases, so discovery is left to run-time tests and even there
an empty string or a zero value may not always trigger the
programmer's attention.

-- 
Marc-Andre Lemburg
eGenix.com

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