Ask Your Question

Difficulties evaluating an expression string

asked 2014-01-24 20:17:42 +0200

Alasdair gravatar image

updated 2014-01-25 17:49:06 +0200

For some recent computations, I devolved some initial calculus to the Maxima sub-system, and I've ended up with a list eqs of Maxima expressions. I want to transfer this list out of Maxima. This works:

sage: eqs2 = [repr(xx) for xx in eqs]

but gives me strings, which are not useful. And this:

sage: eqs2 = [sage_eval(repr(xx)) for xx in eqs]

returns the error message

NameError: name 'a43' is not defined

which is strange, as it is defined as a variable:

sage: a43

I could create a list of local variables:

vars = {'a21':a21,'a31':a31}

and so on, and use


but as there are 20 more variables, this would be tedious.

Is there a better way?

edit retag flag offensive close merge delete


Thanks very much for your answers: I wasn't aware that the `locals` list could be used like this.

Alasdair gravatar imageAlasdair ( 2014-01-25 18:49:22 +0200 )edit

2 Answers

Sort by ยป oldest newest most voted

answered 2014-01-25 14:55:24 +0200

ndomes gravatar image

updated 2014-01-25 18:34:17 +0200

Let sage_eval evaluate in the namespace of the locals dictionary.

expr = sage_eval(xx,locals=locals())

Or do you need something like this:

var_list =['a'+str(k) for k in (11..20)]
vars = dict([(v,var(v)) for v in var_list])
sage_eval('2*a11 +a14^a13-a12',locals=vars)
edit flag offensive delete link more

answered 2014-01-25 14:57:14 +0200

Luca gravatar image

sage_eval does not have access by default to the variables declared in your session. Use the locals keword:

sage: eqs2 = [sage_eval(repr(xx), locals=globals()) for xx in eqs]

Depending on what you want to do, it may be more appropriate to use locals() instead of globals(). See

edit flag offensive delete link more

Your Answer

Please start posting anonymously - your entry will be published after you log in or create a new account.

Add Answer

Question Tools


Asked: 2014-01-24 20:17:42 +0200

Seen: 234 times

Last updated: Jan 25 '14