I'm not 100% clear on the intent of the code, but if you are trying to
discourage users from replacing existing attributes on the instance, you could
try and catch it all in the __setattr__ of the class:
class Bunch(object):
def __init__(self, *args, **kwargs):
for key, value in kwargs.items():
self.__testAttr(key)
setattr(self, key, value)
def __setattr__(self, key, value):
self.__testAttr(key)
super(Bunch, self).__setattr__(key, value)
def __testAttr(self, key):
if hasattr(self, key):
raise AttributeError("API conflict: '%s' is part " \
"of the '%s' API" % (key, self))
def pretty(self):
text = ""
for key, value in self.__dict__.items():
text += "%s: %s\n" % (key, value)
return text
In this example, we just do our check any time they try and set an attribute on
the instance. In python you can never fully prevent these types of things,
since the language is dynamic and interpreted. But this at least prevents the
most direct approaches.
One thing I notice in your example is that once someone sets a new attribute on
the class, they can never change it again, since it will then fail the test the
next time. If you want the functionality of allowing existing attributes that
the user has added to be changed, you would need to keep track of them in a
list of approved attributes.
On Sep 14, 2013, at 2:33 AM, matthew park wrote:
> Hello there,
>
> I am learning masking case when an object is instanced in a class and if the
> name of the object and
> method's name is same, Type error is raised.
>
> the code is
>
> class Bunch(object):
> def __init__(self, *args, **kwargs):
> for key, value in kwargs.items():
> if hasattr(self, key):
> raise AttributeError("API conflict: '%s' is part of the '%s'
> API" % (key, self))
> else:
> setattr(self, key, value)
>
> def pretty(self):
> text = ""
> for key, value in self.__dict__.items():
> text += "%s: %s\n" % (key, value)
> return text
>
> if __name__ == "__main__":
> b = Bunch(pretty=True)
>
>
> The point is I don't know how to set up' bunch.pretty = True ' to prove
> mistake in the following sentences below.
> There, the code triggered a TypeError exception because the Bunch class's
> pretty() method was masked by a data attribute on the instance, which we then
> attempted to call. While the Bunch class now protects this from happening
> during object instantiation, there is nothing to prevent you from masking the
> pretty() method simply by setting bunch.pretty = True after creating an
> instance.
>
>
> Can you give me an example code how to prove nothing to prevent the code
> from masking pretty() method
> simple by setting bunch.pretty=True?
>
>
> Thank you very much for your help!
>
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