Alex Ghitza schrieb:
On Mon, 19 Apr 2010 13:09:34 +0200, bb <[email protected]> wrote:
Tnx!
Is there any explanation why the magic ends with del ?
sage: del x
sage: x
---------------------------------------------------------------------------
NameError Traceback (most recent call last)
/home/bb/sage-4.3.5/local/lib/python2.6/site-packages/sage/all_cmdline.pyc
in <module>()
NameError: name 'x' is not defined
sage:
So the feature theses fits like a glove?
A very popular feature is introspection. In this particular case, doing
sage: reset?
would tell you what reset does:
"Delete all user defined variables, reset all globals variables back to
their default state, and reset all interfaces to other computer algebra
systems."
The feature that Harald was referring to is that x is a predefined
global variable. You know this by doing
sage: globals()['x']
x
So now we know what the Sage function "reset" does. "del", on the other
hand, is a Python builtin function. Googling "del python" gives that
"del can also be used to delete entire variables".
So "del x" deletes the global variable from globals():
sage: del x
sage: globals()['x']
---------------------------------------------------------------------------
KeyError Traceback (most recent call last)
/home/ghitza/<ipython console> in <module>()
KeyError: 'x'
But if you reset again, x is back:
sage: reset
sage: globals()['x']
x
And everything is behaving exactly as the docstrings indicate.
Alex
Thank you very much for your help!
I found that this explanation also holds for the global variable "_"!
Reagrds BB
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