A class with eventhandlers ?

[Runsun Pan]

Is it possible to code a class that raise exception
automatically when an error occurs?

We usually use try-except pair at where we expect an
error might occur. What am thinking is a class that
has built in error handling so we can do this:

c=MyClass()
c.onError = some_hook

or

c.onError('IndexError', IndexErrorHook)

or, more specific, a function/method-specific error
handling feature:

c.load.onError( IOErrorHook)
c.load( filename )

Is there such a mechnism around? If not, is it possible
to make such a thing ?

--
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Runsun Pan, PhD
py********@gmail.com
Nat'l Center for Macromolecular Imaging
http://ncmi.bcm.tmc.edu/ncmi/
~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~*~

[Alex Martelli]

Runsun Pan <py********@gmail.com> wrote:
...

or, more specific, a function/method-specific error
handling feature:

c.load.onError( IOErrorHook)
c.load( filename )

Is there such a mechnism around? If not, is it possible
to make such a thing ?

Never heard of one, but you could surely make a custom metaclass
satisfying your specs (==wrapping each method into an instance of a type
providing such an onError method, as well as a __call__ delegating to
the real method within a suitable try/except). Sounds like a lot of
work to me, though;-).
Alex

[Farshid Lashkari]

It's definitely possible, here's a small example. There are probably
better ways to do it, but I'll let you figure that out ;)

class ErrorHandler:
def __init__(self,method):
self.method = method
self.errorHook = None

def onError(self,hook):
self.errorHook = hook

def __call__(self, *args, **kwargs):
if self.errorHook:
try:
self.method(*args,**kwargs)
except Exception, e:
self.errorHook(e)
else:
self.method(*args,**kwargs)
class MyClass:
def __init__(self):
self.load = ErrorHandler(self.load)

def load(self,filename):
return self.x

def IOErrorHook(e):
print 'Caught error:',e

c = MyClass()
c.load.onError(IOErrorHook)
c.load('filename')