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Python class instantiation using name

Bengt Richter bokr at oz.net
Tue Dec 17 19:41:49 EST 2002 
On Tue, 17 Dec 2002 13:38:06 -0800, Amol P Dharmadhikari <ad at cs.usfca.edu> wrote:

>Hi All,
>
>I have a question about python, which I did not find answered in
>the FAQs and tutorials.
>
>Is it possible to create an instance of a class using its name?
>If so how?
>
>So in general, if I have a string which contains the name of a class,
>how do I create an instance of that class?
>
>i.e. something similar to what the below java code snippet can do
>Object o = java.lang.Class.forName(className).newInstance()
>
>Please cc me in the reply as I am not subscribed to the list.
Ok, just this once, but in future you can see the latest of this newgroup via google:

    http://groups.google.com/groups?hl=en&group=comp.lang.python

with not much delay from posting time. Maybe faster than some long
paths of news forwarding.
>

The following is not tested any more than you see here ;-)

 >>> def classForName(name, *args, **kw):
 ...     ns = kw.get('namespace',globals())
 ...     return ns[name](*args)
 ...
 >>> classForName('B')
 <__main__.B instance at 0x007E1590>
 >>>
 >>> class A: pass
 ...
 >>> class B:
 ...     def __init__(self, *args):
 ...         print 'B init got',args
 ...         self.args = args
 ...
 >>> classForName('A')
 <__main__.A instance at 0x007E1530>
 >>> binst = classForName('B', 123, 'args to B', 456)
 B init got (123, 'args to B', 456)
 >>> binst.args
 (123, 'args to B', 456)
 >>> import types
 >>> classForName('IntType', 123, namespace=types.__dict__)
 123
 >>> classForName('FloatType', 123, namespace=types.__dict__)
 123.0

Regards,
Bengt Richter
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