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sax.handler.Contenthandler.__init__

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  sax.handler.Contenthandler.__init__ Neil Cerutti <neilc@norwich.edu> - 2013-08-30 17:20 +0000
    RE: sax.handler.Contenthandler.__init__ "Prasad, Ramit" <ramit.prasad@jpmorgan.com.dmarc.invalid> - 2013-08-30 17:35 +0000

#53305 — sax.handler.Contenthandler.__init__

This code is from The Python Cookbook, 2nd edition, 12.2 Counting
Tags in a Document:

from xml.sax.handler import ContentHandler
import xml.sax
class countHandler(ContentHandler):
    def __init__(self):
        self.tags={}
    def startElement(self, name, attr):
        self.tags[name] = 1 + self.tags.get(name, 0)

Isn't overriding __init__ a risky thing to do? The docs don't
mention it as a method I should override, and also don't define
what's in there or if I'd need to call the base class __init__.
Moreover, startDocument is provided for parser setup.

As it happens, ContentHandler.__init__ isn't empty, so the above
code could fail if the parser isn't prepared for _locator to be
undefined.

Is the above code is an acceptable idiom?

-- 
Neil Cerutti

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#53307

Neil Cerutti wrote:
> This code is from The Python Cookbook, 2nd edition, 12.2 Counting
> Tags in a Document:
> 
> from xml.sax.handler import ContentHandler
> import xml.sax
> class countHandler(ContentHandler):
>     def __init__(self):
>         self.tags={}
>     def startElement(self, name, attr):
>         self.tags[name] = 1 + self.tags.get(name, 0)
> 
> Isn't overriding __init__ a risky thing to do? The docs don't
> mention it as a method I should override, and also don't define
> what's in there or if I'd need to call the base class __init__.
> Moreover, startDocument is provided for parser setup.
> 
> As it happens, ContentHandler.__init__ isn't empty, so the above
> code could fail if the parser isn't prepared for _locator to be
> undefined.
> 
> Is the above code is an acceptable idiom?
> 
> --
> Neil Cerutti
> --

I think this is a bad idea unless you want to avoid the parent 
class __init__ specifically (in which case a comment stating 
why is mandatory). I do not like that this recipe shows behavior
that might be fine in this instance, but is not a good general 
practice.

     def __init__(self):
         super(ContentHandler, self).__init__()
         #OR ContentHandler.__init__(self)
         self.tags={}

I personally think the super() line is better of the two options.

~Ramit



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