Martin v. Löwis wrote:
> [EMAIL PROTECTED] schrieb:
> > the string class's "nil" value. Each of the builtin types has such an
> > "empty" or "nil" value:
> >
> > string ""
> > list []
> > tuple ()
> > dict {}
> > int 0
> > float 0.0
> > complex 0j
> > set set()
> >
> > Any other value besides the above will compare as "not false".
>
> This list of values that are considered false is incomplete,
> though. Four obvious omissions are
>
> long 0L
> unicode u""
> bool False
> NoneType None
>
> Not-so-obviously, arbitrary user-defined values can also be
> treated as false: If they implement __nonzero__, they are
> false if False is returned from __nonzero__; otherwise,
> if they implement __len__, they are false if 0 is returned
> from __len__. Under these rules, array.array objects can
> also be false, as can UserList and UserDict objects.
A notable exception are numarray arrays (probably true for numpy too, I
haven't tested it though):
>>> from numarray import array
>>> bool(array([1,2]))
Traceback (most recent call last):
File "<stdin>", line 1, in ?
RuntimeError: An array doesn't make sense as a truth value. Use any(a)
or all(a).
George
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