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    <p>There is no casting as the other answers already explained. You can make subclasses or make modified new types with the extra functionality using <strong>decorators</strong>.</p> <p>Here's a complete example (credit to <a href="https://stackoverflow.com/questions/739654/understanding-python-decorators">How to make a chain of function decorators?</a>). You do not need to modify your original classes. In my example the original class is called Working.</p> <pre><code># decorator for logging def logging(func): def wrapper(*args, **kwargs): print func.__name__, args, kwargs res = func(*args, **kwargs) return res return wrapper # this is some example class you do not want to/can not modify class Working: def Do(c): print("I am working") def pr(c,printit): # other example method print(printit) def bla(c): # other example method c.pr("saybla") # this is how to make a new class with some methods logged: class MutantWorking(Working): pr=logging(Working.pr) bla=logging(Working.bla) Do=logging(Working.Do) h=MutantWorking() h.bla() h.pr("Working") h.Do() </code></pre> <p>this will print</p> <pre><code>h.bla() bla (&lt;__main__.MutantWorking instance at 0xb776b78c&gt;,) {} pr (&lt;__main__.MutantWorking instance at 0xb776b78c&gt;, 'saybla') {} saybla pr (&lt;__main__.MutantWorking instance at 0xb776b78c&gt;, 'Working') {} Working Do (&lt;__main__.MutantWorking instance at 0xb776b78c&gt;,) {} I am working </code></pre> <p>In addition, I would like to understand why you can not modify a class. Did you try? Because, as an <strong>alternative</strong> to making a subclass, if you feel dynamic you <em>can</em> almost always modify an old class in place:</p> <pre><code>Working.Do=logging(Working.Do) ReturnStatement.Act=logging(ReturnStatement.Act) </code></pre> <p>Update: <strong>Apply logging to all methods of a class</strong></p> <p>As you now specifically asked for this. You <em>can</em> loop over all members and apply logging to them all. But you need to define a rule for what kind of members to modify. The example below excludes any method with __ in its name .</p> <pre><code>import types def hasmethod(obj, name): return hasattr(obj, name) and type(getattr(obj, name)) == types.MethodType def loggify(theclass): for x in filter(lambda x:"__" not in x, dir(theclass)): if hasmethod(theclass,x): print(x) setattr(theclass,x,logging(getattr(theclass,x))) return theclass </code></pre> <p>With this all you have to do to make a new logged version of a class is:</p> <pre><code>@loggify class loggedWorker(Working): pass </code></pre> <p>Or modify an existing class in place:</p> <pre><code>loggify(Working) </code></pre>
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    1. POHow to cast object in Python
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    1. USJohan Lundberg
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    1. COI think you understood my problem and this far this seems to be THE answer. Thank you!
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      1. USVisko
    2. COAfter my initial enthusiasm I sadly realized that this is not a solution for my problem. I can't modify the Working class using decorators to return MutantReturnStatement instead of ReturnStatement, because that was the initial condition (Working can't be modified).
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    3. CO@Visko, I think you misread my answer then. My 'loghello' is exactly the 'MutantWorking' you asked for. You do not have to modify 'Working' just as I did not modify 'hello'. If you think this is still unclear or if you don't agree I can try to update my answer.
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