To avoid confusion use "symbol" instead of "symbolic variable". A Python
variable is a variable in the sense of programming
https://en.wikipedia.org/wiki/Variable_%28computer_science%29
A symbol represents a mathematical variable as in
https://en.wikipedia.org/wiki/Variable_%28mathematics%29
The following is some Python code that makes available a (Python)
variable outside of a function
def f():
global a
a = 3
f()
print a
But there is *no* such thing as local variable definition in Python. The
command "a = 5" or "t = cos(10.)" is in itself a variable declaration...
which is a bit confusing if you start mixing with symbols and the
terrible var function in Sage. You might have a look at other examples in
http://www.python-course.eu/python3_global_vs_local_variables.php
On 21/12/15 21:12, Carl Eberhart wrote:
Thanks
I guess I don't understand the difference between a python variable and a
symbolic variable.
I know that var is part of Sage but not defined in python.
I also know that the variables created inside a sage procedure using SR.var
are local, but ones created by var are not.
So inside of procedures, use SR.var, not var, unless you want them to be
available outside the procedure.
Is that correct Jeroen?
On Monday, December 21, 2015 at 5:09:05 PM UTC-6, vdelecroix wrote:
No. You can try
Still
def f():
var('whatever')
f()
print whatever StillThanks.
SR.var does the trick for me inside of procedures. var doesn't
Nothing to do with the fact that 't' was globally available before.
By design the function var:
- creates a new symbolic variable (*not* a Python variable)
- makes it available in the global namespace as a Python variThanks.
SR.var does the trick for me inside of procedures. var doesn'table
under the same namStille
Some more examples:
t = 5 Still
-> creates a Python variable named t which contains 5
Still
t = SR.var('x')
-> creates a Python variable named t which contains a symbolic
variable named x Still
var('t')
-> creates a Python variable named t which contains a symbolic
variable named t.
Indeed the latter should really be thought as
t = SR.var('t') StillThanks.
SR.var does the trick for me inside of procedures. var doesn't
Vincent
On 21/12/15 14:35, Carl Eberhart wrote: Thanks.
SR.var does the trick for me inside of procedures. var doesn't
Ah. Thanks very much for that clarification.
Actually, my snippet illustrates the dilemma I was in.
t already has a value outside of f
executing f changes the value of t outside of f
that is what I would expect to happen if t were declared global in f,
but I
thought t was local in f
I still love var, but now I know when to use SR.var instead
Carl Thanks.
SR.var does the trick for me inside of procedures. var doesn't
On Mon, Dec 21, 2015 at 9:49 AM, Jeroen Demeyer <jdem...@cage.ugent.be
<javascript:>>
wrote:
On 2015-12-21 16:38, Carl Eberhart wrote:
I admit I don't understand what is happening in the following snippit:
def f():
t=var('t')
t=5
a=2*t
return a
Solution: never use var() in a function. If you do need a symbolic
variable in a function (note that you don't in the snippet above), you
can
use SR.var() instead of plain var(). That behaves like var(), except
that
it does not change any global. Example:
sage: SR.var('y')
y
sage: y
NameError: name 'y' is not defined
You can use it with explicit assignment:
sage: y = SR.var('y')
sage: y
y
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