Re: Accessing 'mangled' class attrbutes
Gerard Flanagan wrote: I would like to do the following: from elementtree.SimpleXMLWriter import XMLWriter class HtmlWriter(XMLWriter, object): def write_raw(self, text): super( HtmlWriter, self ).flush() super( HtmlWriter, self ).__write(text) but because of the name-mangling caused by '__write' I get: AttributeError: 'super' object has no attribute '_HtmlWriter__write'. Is there any simple way round this situation in general? (I just want to write out a HTML 'DOCTYPE' declaration) Try: (not the Python keyword, but a directive to you) super(HtmlWriter, self)._XMLWriter__write(text) In general, to access the name-mangled members, simply add _class_name to the front of the member name and you should be able to get at it. But be careful, since this is a reference to the base class, so if it's inherited from some other class, you'll need to know from which class the member is inherited. HTH -- Steve Juranich Tucson, AZ USA -- http://mail.python.org/mailman/listinfo/python-list
Re: Accessing 'mangled' class attrbutes
Is there any simple way round this situation in general? It might be safer to use composition instead of inheritance in this case. Assuming that XMLWriter has a write method to write what you want, you could hold a reference to an XMLWriter within your class and pass along write command like: writer = XMLWriter() writer.write(stuff) -- http://mail.python.org/mailman/listinfo/python-list
Re: Accessing 'mangled' class attrbutes
Steve Juranich wrote: Gerard Flanagan wrote: I would like to do the following: from elementtree.SimpleXMLWriter import XMLWriter class HtmlWriter(XMLWriter, object): def write_raw(self, text): super( HtmlWriter, self ).flush() super( HtmlWriter, self ).__write(text) but because of the name-mangling caused by '__write' I get: AttributeError: 'super' object has no attribute '_HtmlWriter__write'. Is there any simple way round this situation in general? (I just want to write out a HTML 'DOCTYPE' declaration) Try: (not the Python keyword, but a directive to you) super(HtmlWriter, self)._XMLWriter__write(text) In general, to access the name-mangled members, simply add _class_name to the front of the member name and you should be able to get at it. But be careful, since this is a reference to the base class, so if it's inherited from some other class, you'll need to know from which class the member is inherited. HTH -- Steve Juranich Tucson, AZ USA I tried that Steve but it didn't work, and i don't think I can do what I want in any case. There is no method '__write' in the base class, it is only declared as an instance attribute in the constructor, like so: def __init__(self, file, encoding=us-ascii): ... self.__write = file.write ... I tried putting '__write = None' at the class level (in the base class XMLWriter) but then, although '_XMLWriter__write' appears in 'dir(HtmlWriter)', I get 'NoneType is not callable'. I also tried 'def __write(self, text) : pass ' in the base class, but then the code runs but doesn't write the text I want - and anyway, if I'm going to change the base class, then i may as well just add the 'write_raw' method to the base directly! It's just some toy code at any rate, and I've learnt something new! Thanks for your reply. Gerard -- http://mail.python.org/mailman/listinfo/python-list
Re: Accessing 'mangled' class attrbutes
[EMAIL PROTECTED] wrote: Is there any simple way round this situation in general? It might be safer to use composition instead of inheritance in this case. Assuming that XMLWriter has a write method to write what you want, you could hold a reference to an XMLWriter within your class and pass along write command like: writer = XMLWriter() writer.write(stuff) No, XMLWriter doesn't have a 'write' method, if it did I could have done: super(HtmlWriter, self).write(stuff) I think the XMLWriter class has been designed so you can't just write any old text because this better ensures that tags are properly closed and so on. There is a public 'data' method: writer.data( text ) but it escapes angle brackets, and what i wanted was to write '!DOCTYPE.'. Thanks Gerard -- http://mail.python.org/mailman/listinfo/python-list
Re: Accessing 'mangled' class attrbutes
Gerard Flanagan wrote: I tried that Steve but it didn't work, and i don't think I can do what I want in any case. There is no method '__write' in the base class, it is only declared as an instance attribute in the constructor, like so: def __init__(self, file, encoding=us-ascii): ... self.__write = file.write ... I tried putting '__write = None' at the class level (in the base class XMLWriter) but then, although '_XMLWriter__write' appears in 'dir(HtmlWriter)', I get 'NoneType is not callable'. I also tried 'def __write(self, text) : pass ' in the base class, but then the code runs but doesn't write the text I want - and anyway, if I'm going to change the base class, then i may as well just add the 'write_raw' method to the base directly! It's just some toy code at any rate, and I've learnt something new! Thanks for your reply. Gerard Make sure you're calling the super's constructor before you try and access the mangled member. Then (I forgot this part), you can just call the mangled member from `self'. Example follows. foo.py class A(object): def __init__(self): self.__foo = lambda x, y : x + y class B(A): def __init__(self, x, y): # Make sure you're calling the super's constructor first. super(B, self).__init__() self.sum = self._A__foo(x, y) /foo.py import foo b = foo.B(3, 4) b.sum 7 -- Steve Juranich Tucson, AZ USA -- http://mail.python.org/mailman/listinfo/python-list
Re: Accessing 'mangled' class attrbutes
Steve Juranich wrote: Gerard Flanagan wrote: I tried that Steve but it didn't work, and i don't think I can do what I want in any case. There is no method '__write' in the base class, it is only declared as an instance attribute in the constructor, like so: def __init__(self, file, encoding=us-ascii): ... self.__write = file.write ... I tried putting '__write = None' at the class level (in the base class XMLWriter) but then, although '_XMLWriter__write' appears in 'dir(HtmlWriter)', I get 'NoneType is not callable'. I also tried 'def __write(self, text) : pass ' in the base class, but then the code runs but doesn't write the text I want - and anyway, if I'm going to change the base class, then i may as well just add the 'write_raw' method to the base directly! It's just some toy code at any rate, and I've learnt something new! Thanks for your reply. Gerard Make sure you're calling the super's constructor before you try and access the mangled member. Then (I forgot this part), you can just call the mangled member from `self'. Example follows. foo.py class A(object): def __init__(self): self.__foo = lambda x, y : x + y class B(A): def __init__(self, x, y): # Make sure you're calling the super's constructor first. super(B, self).__init__() self.sum = self._A__foo(x, y) /foo.py import foo b = foo.B(3, 4) b.sum 7 -- Steve Juranich Tucson, AZ USA It's all becoming clear! Yes, calling the base constructor was all I needed to do: class HtmlWriter(elementtree.SimpleXMLWriter.XMLWriter, object): def __init__(self, file): super( HtmlWriter, self).__init__(file) def write_raw(self, text): self.flush() self._XMLWriter__write(text) -works a charm. Appreciate your help Steve, thanks again. Gerard -- http://mail.python.org/mailman/listinfo/python-list
