undo a dictionary

Kay Schluehr kay.schluehr at gmx.net
Wed Jul 30 17:22:56 CEST 2008

On 30 Jul., 16:51, mmm <mdbol... at gmail.com> wrote:
> I found code to undo a dictionary association.
> def undict(dd, name_space=globals()):
>     for key, value in dd.items():
>         exec "%s = %s" % (key, repr(value)) in name_space
> So if i run
> >>> dx= { 'a':1, 'b': 'B'}
> >>> undict(dx)
> I get>>> print A, B
> 1 B
> Here,  a=1 and b='B'
> This works well enough for simple tasks and I understand the role of
> globals() as the default names space, but creating local variables is
> a problem.

Python is lexically scoped. You can't create locals at runtime.

> Also having no output arguemtns to undict() seems
> counterintuitive.  Also, the function fails if the key has spaces or
> operand characters (-,$,/,%).

Python names can't have punctuation with the exception of underscores.

> Finally I know I will have cases where
> not clearing (del(a,b)) each key-value pair might create problems in a
> loop.
> So I wonder if anyone has more elegant code to do the task that is
> basically the opposite of creating a dictionary from a set of
> globally assigned variables.  And for that matter a way to create a
> dictionary from a set of variables (local or global).  Note I am not
> simply doing and  undoing dict(zip(keys,values))

May I ask what's wrong with having namespaces in a language?

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