How Do You Replace Variables With Their Values?

[Chris Angelico]

On Mon, Jul 15, 2019 at 5:45 AM Ian Kelly <ian.g.kelly at gmail.com> wrote:
>
> On Thu, Jul 11, 2019 at 11:10 PM Chris Angelico <rosuav at gmail.com> wrote:
> >
> > On Fri, Jul 12, 2019 at 2:30 PM Aldwin Pollefeyt
> > <aldwinaldwindev at gmail.com> wrote:
> > >
> > > Wow, I'm so sorry I answered on the question : "How do you replace a
> > > variable with its value". For what i understood with the example values,
> > > CrazyVideoGamez wants 3 variables named like the meal-names in
> dictionary.
> > > Yes, it's not secure unless you work with your own dataset (just like
> > > sending your own created commands with set=True in subprocess). Yes
> there
> > > might be better solutions for the real problem. But maybe the user
> really
> > > has a purpose for it, in a secure environment with own datatset, it's a
> > > valid answer for "How do you replace a variable with its value".
> > >
> >
> > What you gave was dangerous advice, and yes, there IS a better
> > solution - and an easier one. If you want to create variables
> > dynamically, then just create them!
> >
> > for meal, parts in dinner.items():
> >     globals()[meal.replace(' ','_')] = dinner[meal]
> >
> > Python has a rich set of metaprogramming tools. Don't just always
> > reach for exec and caveat it with "it's okay if you trust everything".
>
> To be fair, if dinner is untrusted then this new version is still unsafe.
> You've just allowed it to shadow any global or built-in it wants to.

This is true, but that risk is in the original too. What I'd ACTUALLY
do, in this sort of situation, would be to make some sort of namespace
object, so I can write foo.Desert rather than using square bracket
notation; otherwise, though, I'd just stick with the original.

But if you want to unpack an object into a namespace, it's certainly
better to assign directly into the namespace than to eval.

ChrisA