modifying vars() dictionary?

[Remco Gerlich]

Lance E Sloan <lsloan at umich.edu> wrote in comp.lang.python:
> In the documentation, it says about vars():
> 
>     The returned dictionary should not be modified: the effects on
>     the corresponding symbol table are undefined.
> 
> Why are the effects undefined?  Why doesn't it always work to set
> a value for variable 'x' by assigning that value to the 'x' element
> of the dictionary from vars()?

Because you're not supposed to set things in it, and whether it works or not
at the moment is a complete accident of implementation that might change at
any moment.

I never understand why people need this functionality, but if you really
need it you can always use exec, or setattr() on a module or instance.

> I've noticed that sometimes it works and sometimes it doesn't. In my
> small example it worked, but a colleague who asked me about this
> couldn't get it to work in a larger program.  I assume that I'm just
> lucky mine worked and that his problem may have something to do with
> the size of the symbol table or the kinds of objects in it.

Or the phase of the moon. It's *undefined*.

-- 
Remco Gerlich