Question about None
steve at REMOVETHIS.cybersource.com.au
Sat Jun 13 02:29:34 EDT 2009
Paul LaFollette wrote:
> 3) (this is purely philosophical but I am curious) Would it not be
> more intuitive if
> isinstance(None, <anything at all>) returned true?
Good grief no!!!
None is an object. It has a type, NoneType. It's *not* a string, or a float,
or an int, or a list, so why would you want isinstance() to *lie* and say
that it is?
Python is good for testing these sorts of ideas:
>>> _isinstance = isinstance
>>> def isinstance(obj, type):
... if obj is None: return True
... return _isinstance(obj, type)
>>> x = "parrot"
>>> if isinstance(x, str):
... print x.upper()
>>> x = None
>>> if isinstance(x, str): print x.upper()
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
AttributeError: 'NoneType' object has no attribute 'upper'
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