namespace hacking question

Fuzzyman fuzzyman at gmail.com
Fri Oct 1 14:12:51 CEST 2010


On Sep 30, 6:07 pm, kj <no.em... at please.post> wrote:
> This is a recurrent situation: I want to initialize a whole bunch
> of local variables in a uniform way, but after initialization, I
> need to do different things with the various variables.
>
> What I end up doing is using a dict:
>
> d = dict()
> for v in ('spam', 'ham', 'eggs'):
>     d[v] = init(v)
>
> foo(d['spam'])
> bar(d['ham'])
> baz(d['eggs'])
>
> This is fine, but I'd like to get rid of the tedium of typing all
> those extra d['...']s.
>
> I.e., what I would *like* to do is something closer to this:
>
> d = locals()
> for v in ('spam', 'ham', 'eggs'):
>     d[v] = init(v)
>
> foo(spam)
> bar(ham)
> baz(eggs)
>
> ...but this results in errors like "NameError: global name 'spam' is
> not defined".
>
> But the problem is deeper than the fact that the error above would
> suggest, because even this fails:
>
> spam = ham = eggs = None
> d = locals()
> for v in ('spam', 'ham', 'eggs'):
>     d[v] = init(v)
>
> foo(spam) # calls foo(None)
> bar(ham)  # calls bar(None)
> baz(eggs) # calls baz(None)
>
> In other words, setting the value of locals()['x'] does not set
> the value of the local variable x.
>
> I also tried a hack using eval:
>
> for v in ('spam', 'ham', 'eggs'):
>     eval "%s = init('%s')" % (v, v)
>
> but the "=" sign in the eval string resulted in a "SyntaxError:
> invalid syntax".
>
> Is there any way to use a loop to set a whole bunch of local
> variables (and later refer to these variables by their individual
> names)?
>

One way:

import sys
module = sys.modules[__name__]

for entry in ('spam', 'eggs', 'ham'):
    setattr(module, entry, 'some value')


Michael Foord
--
http://www.voidspace.org.uk/



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