I don't know how "clean" it is, but there are a few situations in which I do something like this:
getattr(obj, "method", default_method)(*original_method_args) The default_method is a base implementation or a simple error handler. For example, when a client hits one of our XMLRPC servers and passes a method name that's not defined, I've got a default catch-all that logs that and handles the error accordingly. -Jeff On 10/4/07, Grant Edwards <[EMAIL PROTECTED]> wrote: > > On 2007-10-04, Bruno Desthuilliers < > [EMAIL PROTECTED]> wrote: > > > Yes, and it's even simpler : just pass your object. If it effectively > > implements the desired interface, everything will work fine !-) > [...] > > >> What I'd like to do is create a feature detection system for > >> my work -- specifically, a general class / interface called > >> "Feature" and then subclasses that implement functions like > >> isFeaturePresent() in all of their different and unique ways. > >> I'd love to hear how I can do this in Python. > > > > I'm not sure about what you exactly want to do, but FWIW, checking if an > > object has a given attribute is quite simple: > > > > if has_attr(obj, 'attribute_name'): > > print "Hurray" > > else: > > print "D'oh" > > > > Note that in Python, methods are attributes too - only they > > are callable. > > On a slight tangent.... > > The "Pythonic" way to handle things like that is often just > to call the method you want to call. If the object doesn't > have that method, then you catch the exception and do whatever > it is you do in the case where the object doesn't have the > feature in question. > > The tricky bit is only catching the AttributeError exception > generated by the attempt to access the non-existant method, and > not catching AttributeError exceptions generated by bugs in the > method when it does exist. > > Once you've added code to make sure you only catch exceptions > you care about, it's simpler to just call has_attr > > the obvious method > > try: > myobj.feature1() > except AttributeError: > print "object doesn't implement feature1" > > isn't correct, since an unhandled AttributeError generated by > the feature1 method will print "object doesn't implement > feature1". Attempting to isolate the attributeError we care > about looks like this: > > try: > m = myobj.feature1 > except AttributeError: > print "object doesn't implement feature1" > else: > m() > > That's just too messy compared with the has_attr method that > goes like this: > > if has_attr(myobj,'feature1'): > myobj.feature1() > else: > print "object doesn't implement feature1" > > However, I don't like that alot because you've got to supply > the method name twice: once as a string and once as the method > name. > > What's the cleanest way to call a method that might not be > there? > > -- > Grant Edwards grante Yow! My haircut is > totally > at traditional! > visi.com > -- > http://mail.python.org/mailman/listinfo/python-list >
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