sax.handler.Contenthandler.__init__

[Neil Cerutti]

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?

 

[Prasad, Ramit]

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?

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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