Roald de Vries wrote:
On Aug 5, 2010, at 5:42 PM, wheres pythonmonks wrote:
How does "x is not None" make any sense? "not x is None" does make
sense.
I can only surmise that in this context (preceding is) "not" is not a
unary right-associative operator, therefore:
x is not None === IS_NOTEQ(X, None)
Beside "not in" which seems to work similarly, is there other
syntactical sugar like this that I should be aware of?
'not None' first casts None to a bool, and then applies 'not', so 'x is
not None' means 'x is True'.
This is not correct. 'is not' is a single operator, and in this case is
checking that the object 'x' is not the same as the object 'None'. No
boolean conversions are done -- False and True have nothing to do with
this example.
Python 2.5.4 (r254:67916, Dec 23 2008, 15:10:54) [MSC v.1310 32 bit
(Intel)] on win32
Type "help", "copyright", "credits" or "license" for more information.
--> x = 5
--> x is not None
True
--> x = True
--> x is not None
True
--> x = ('this','is','a','tuple')
--> x is not None
True
--> x = None
--> x is not None
False
~Ethan~
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