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Desattribution of a value to a variable

asked 2020-05-12 09:53:36 -0500

Cyrille gravatar image

Suppose I have attributed to a the value 3. But for the following operation I want to use anew a as a variable how should I operate, redefine a ?

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answered 2020-05-12 11:26:32 -0500

tmonteil gravatar image

updated 2020-05-12 11:28:20 -0500

A Python name is just a pointer to a Python/Sage object:

sage: a = 3
sage: a+a
6

Now, if you redefine it, it will just point to the new object:

sage: a = 12
sage: a
12
sage: a^2
144

If you want the symbol a (not to be confused with the Python name a), you can do:

sage: SR.var('a')
a

Any Python name can point to such symbol:

sage: b = SR.var('a')
sage: b
a
sage: (b+1)^2
(a + 1)^2

What confuses most people is that the shortcut:

sage: var('a')
a

both returns the symbol a and let the Python name a point to this symbol, in particular, it removes the previous pointer of the Python name a :

sage: a        # this a is a Python name
a              # this a is a symbol, pointed bythe previous Python name
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Asked: 2020-05-12 09:53:36 -0500

Seen: 33 times

Last updated: May 12