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Developing with the interactive interpreter can be tricky. When your class changes, you need to reload the module and create new objects with the new code.

This recipe offers a simple wrapper which will make reloading a bit easier.

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class ReloadableClass(object):
    def __init__(self, mod_name, cls_name, *args, **kw):
        self._mod_name = mod_name
        self._cls_name = cls_name
        self._args = args
        self._kw = kw

        self._mod = __import__(mod_name)
        self._cls = getattr(self._mod, self._cls_name)

        self._obj = self._cls(*args, **kw)

    def __getattribute__(self, attr):
        try:
            return object.__getattribute__(self, attr)
        except AttributeError:
            return getattr(self._obj, attr)
        raise AttributeError

    def reload(self):
        reload(self._mod)
        self._cls = getattr(self._mod, self._cls_name)

        self._obj = self._cls(*self._args, **self._kw)



# some_mod.py
class TestClass:
    def foo(self):
        print 'foo'
        #print 'bar'
    #def baz(self):
    #    print 'baz'



>>> from reloadable_class import ReloadableClass
>>> c = ReloadableClass('some_mod', 'TestClass')
>>> c.foo()
foo
>>> c.baz()
Traceback (most recent call last):
File "<stdin>", line 1, in ?
File "reloadable_class.py", line 34, in __getattribute__
    return getattr(self._obj, attr)
AttributeError: TestClass instance has no attribute 'baz'
>>> c.reload() # after making changes to TestClass
>>> c.foo()
foo
bar
>>> c.baz()
baz

As written, this wrapper simply replaces the old object with a fresh new one. None of the old state is saved. Copying of state from the old object to the new one could be added.

Other solutions involve metaclasses (http://aspn.activestate.com/ASPN/Cookbook/Python/Recipe/160164) or a background watcher thread (http://aspn.activestate.com/ASPN/Mail/Message/python-list/907876)

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Created by Lee Harr on Sun, 3 Dec 2006 (PSF)
Python recipes (4193)
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