None, False, True
Gregor Lingl
glingl at aon.at
Wed Sep 17 17:00:23 EDT 2003
M-a-S schrieb:
> Can anybody explain this:
>
> Python 2.3 (#46, Jul 29 2003, 18:54:32) [MSC v.1200 32 bit (Intel)] on win32
> Type "help", "copyright", "credits" or "license" for more information.
>
>>>>None = 3
>
> <stdin>:1: SyntaxWarning: assignment to None
>
Interestingly this doesn't occur in IDLE:
Python 2.3 (#46, Jul 29 2003, 18:54:32) [MSC v.1200 32 bit (Intel)] on win32
Type "copyright", "credits" or "license()" for more information.
...
IDLE 1.0
>>> None = 3
SyntaxError: assignment to None (<pyshell#0>, line 1)
>>> print None
None
In a recent posting to this list I asked how to write-protect
names. This seems to be done here with the Name None.
But again: how is it done?
----
On the other side the existence and knowledge of the None-object
doesn't disappear completely in the plain Python interpreter:
>>> None = 3
<stdin>:1: SyntaxWarning: assignment to None
>>> None
3
>>> def f():
... pass
...
>>> print f()
None
But:
>>> def g():
... return None
...
>>> g()
3
So you can use f to restore the value of None
(if you happened to forget to save it):
>>> None = f()
<stdin>:1: SyntaxWarning: assignment to None
>>> None
>>> print None
None
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