David, Oscar,
Thank you for your help.
Oscar, the list 'u' was created in the course of a calculation, and
saved as a .pkl file. I then reloaded it and want to manipulate the
saved equations, of which u[7] is an example. I found an even cleaner
example, see below.
I have the impression that when the .pkl file was reloaded, the identity
of the object
Symbol('a', real=True, positive=True)
contained within u[3] was set to a memory address and when I created the
object
Symbol('a', real=True, positive=True)
in the current session, that was left pointing to a *different* address.
(See below.)
I can use "id(a)" to see what address the "current session variable a"
is pointing to. Is there a simple way for me to understand what address
a=Symbol('a',real=True,positive=True) in the u[3] object is pointing to?
Presumably these are different, even though the two variables have the
same name and the same properties.
If that behavior is correct, I may need some help to revise my mental
model of how sympy/python works (:-).
Cheers,
Bruce
>>> u[3]
2*a
>>> srepr(u[3])
"Mul(Integer(2), Symbol('a', real=True, positive=True))"
>>> x=2*a
>>> srepr(x)
"Mul(Integer(2), Symbol('a', real=True, positive=True))"
>>> x==u[3]
False
On 07.04.21 14:05, David Bailey wrote:
On 07/04/2021 12:28, Oscar Benjamin wrote:
In Bruce's example both symbols seem to have the same assumptions so
this shouldn't be the issue.
Oscar
I just checked and you can make two non-identical symbols that way:
Symbol('a')+Symbol('a',Positive=True)
a + a
I almost wonder if that should not flag an error.
David
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