Argument of the bool function

Mel mwilson at the-wire.com
Fri Apr 8 18:42:22 CEST 2011


candide wrote:
> About the standard function bool(), Python's official documentation 
> tells us the following :
>
> bool([x])
> Convert a value to a Boolean, using the standard truth testing procedure.
>
> In this context, what exactly a "value" is referring to ?
>
> For instance,
>  >>> x=42
>  >>> bool(x=5)
> True
>  >>>

Cute.  What's happening here is that `x=5` isn't really an expression. 
It's passing a value to the named parameter `x`, specified in the
definition of `bool`.  Try it with something else:

Python 2.6.5 (r265:79063, Apr 16 2010, 13:09:56) 
[GCC 4.4.3] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> bool(y=5)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'y' is an invalid keyword argument for this function



Mel.



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