Python newbie with a problem writing files

[limodou]

On 4 Sep 2006 08:16:24 -0700, Jason <tenax.raccoon at gmail.com> wrote:
> limodou wrote:
> > > Code:
> > >
> > > import feedparser
> > > from xml.sax import saxutils
> > >
> > > feed_number=200
> > >
> > > feed_list = open("feed_listing.conf","r")
> > > for each_feed in feed_list:
> > >     data=feedparser.parse(each_feed)
> > >     feed_title=data.entries[0].title
> > >     xml_output=open("xml_data\\feed" + str(feed_number) + ".xml", "w")
> >
> > Maybe there is a extra '=', if it should be:
> >
> > xml_output.write(feed_title)
> >
> > ?
> >
>
> It took me a few moments to parse what limodou wrote here, but he's
> absolutely correct.  Your problem is that you are trying to reassign
> the write method in your file.  File objects are built-in types, and do
> not allow their methods to be calvaliery replaced.
>
> Here's an example on the correct way (and your way) of writing to a
> file:
> >>> f = open('spam.xml', 'w')
> >>> f.write( 'This data is written to the file' )
> >>> f.write = ("This is not a valid Python syntax")
> Traceback (most recent call last):
>   File "<stdin>", line 1, in ?
> AttributeError: 'file' object attribute 'write' is read-only
> >>>
>
> You'll notice that the AttributeError describes exactly what's wrong in
> this case.  The write method on your file attribute is read-only.  It
> doesn't say anything about whether your file is read-only.
>
> If you really, really want to change the write method into a string,
> you can subclass from the file class:
>
> >>> class MyFileType(file):
> ...     pass
> ...
> >>> myfile = MyFileType('spam_and_eggs.xml', 'w')
> >>> myfile.write
> <built-in method write of MyFileType object at 0x00870B88>
> >>> myfile.write = "Gonna replace write method with this string!"
> >>> myfile.write
> 'Gonna replace write method with this string!'
> >>>
>
> Of course, you can no longer easily access the original write method
> after re-assigning it like that.
>
> (limodou, I thought this might need a little bit of extra explanation
> for the original poster.  I apologize if I seem rude here.)
>
Very good, I just want to point out the bug according to the
traceback, and don't think so much. But you explained so details.

:)

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