How to name class instances after an iterable keys?

Question

I'd like to create instances of classes getting their names from list values or dictionaries keys or values. Basically what I'd like to do is:

iter = ['foo', 'bar']
for a in iter:
    a = Cls()

and get foo and bar instances of Cls() class instead of having instance referenced by a updated at each loop.

Thanks in advance.

So you want `foo` and `bar` to be local variables? Or is Cédric's answer okay? — Ray Toal, Jul 21 '11 at 08:14
If what Ray wrote is, what you are looking for, then the answer is: You better don't! — phant0m, Jul 21 '11 at 08:16

score 7 · Answer 1 · answered Jul 21 '11 at 08:07

7

Maybe with a dictionnary :

iter = ['foo', 'bar']
result = {}
for a in iter:
    result[a] = Cls()

And in result you'll have { 'foo' : instance_of_Cls, 'bar' : instance_of_Cls}

answered Jul 21 '11 at 08:07

Cédric Julien

3

Shorter: `result = dict((name, Cls()) for name in iter)`. +1. – Fred Foo Jul 21 '11 at 08:12
@cedric this is what I'm using but I'd like to have foo.attr and foo.meth instead of result['foo'].attr etc. This is much readable and avoids messing with wrapping containers. Thank you anyway. – silopolis Jul 21 '11 at 08:42
@Silopolis : to do what you want, you'll have to modify your locals() dictionnary, and this is not a good solution... Why your variables have to be defined by strings ? – Cédric Julien Jul 21 '11 at 08:45
@cedric: actually, they don't "have to" as my code is running with the dict_of_objects trick but I wished I could make it clearer and had liked to be able to create series of objects which names are only known at config/runtime without the container hack... But this leads me to the question: if it had been possible, could I then easily access the list of instances ? reading this http://stackoverflow.com/questions/328851/python-printing-all-instances-of-a-class , it seems that embedding instances in a container is way easier. Thanks a lot :-) – silopolis Jul 21 '11 at 09:10
... and finally, reading http://docs.python.org/library/weakref.html, IIUC, this could be even better to use `weakref.WeakValueDictionary()` in this case so that the list is dynamic and the objects can be garbage collected. – silopolis Jul 21 '11 at 09:34

score -1 · Answer 2 · answered Jul 21 '11 at 08:07

-1

You could use dynamic code evaluation.

inst1 = eval("foo()")
inst2 = eval(a + "()")
inst3 = eval(a)()

answered Jul 21 '11 at 08:07

ron

Maybe I misunderstood the question. – ron Jul 21 '11 at 08:09
My problem was getting inst1/2/3 from a list or dict. My question also applies if you'd wanted to create a series of dicts, or lists or whatever, getting their names from another container. – silopolis Jul 21 '11 at 09:31

2 Answers2