python dynamic class names

Question

Trying to instantiate a class based on a string value and... failing. The parser object below is a dict, in the example let's say we have one called foo and here parser['name'] is 'foo':

obj = parser['name']()

Fails, yielding TypeError: 'str' object is not callable. But, since I have:

class foo:
    def __init__(self():
        print 'Hello'

And if I do obj = foo() it works fine and creates the correct object. Also, calling obj = type(parser['name'])() doesn't work.

How to resolve this? Update: I don't really want to use a mapping system: the names of these classes are defined INI files, and parsed that way, so they will be strings..

Answer 1

As answered in:
Python dynamic class names

There is an easier way to do this if you know which module the classes are defined in, for example:

getattr(my_module, my_class_name)()

Answer 2

classmap = {
  'foo': foo
}

obj = classmap[parser['name']]()

Answer 3

The type(name, bases, dict) built-in function is the correct way to dynamically construct classes--especially when given strings for class names. See the documentation here: http://docs.python.org/library/functions.html#type

In you particular example, it might look like this:

>>> def init(self):
...     print 'Hello'
...
>>> Foo = type('Foo', (object,), {'__init__': init})
>>> foo = Foo()
Hello