Suggestion in Issue #12052 (Better input validation for nsolve)

[Mohit Raj]

Hey all,
I would like to have any valuable suggestions on this code below.
It is maintaining order of variables. I think preorder_traversal would also work.
Kindly do give suggestions on this.

if fargs is None:
            fargs = [ ]
            seen = [ ]
            out = [ ]   
            for i in f:
                temp = i.as_ordered_terms()
                for j in temp:
                    if(isinstance(j,Symbol)):
                        out.append(j)
        for m in out:
            if m not in seen:
                fargs.append(m)
                seen.append(m)

[Aaron Meurer]

It is possible to canonically order Symbols, but that order is
completely arbitrary, and might not be what the user expects. It's
best to require the user to specify the symbol order, so there is no
ambiguity.

Aaron Meurer

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