[New-bugs-announce] [issue13633] Handling of hex character references in HTMLParser.handle_charref

[Ezio Melotti]

New submission from Ezio Melotti <ezio.melotti at gmail.com>:

The doc for handle_charref and handle_entityref say:
"""
HTMLParser.handle_charref(name)
    This method is called to process a character reference of the form "&#ref;". It is intended to be overridden by a derived class; the base class implementation does nothing.

HTMLParser.handle_entityref(name)
    This method is called to process a general entity reference of the form "&name;" where name is an general entity reference. It is intended to be overridden by a derived class; the base class implementation does nothing.
"""

The doc doesn't mention hex references, like "&#x3E;", and apparently they are passed to handle_charref without the '&#' but with the leading 'x':

>>> from HTMLParser import HTMLParser
>>> class MyParser(HTMLParser):
...   def handle_charref(self, data):
...     print data
... 
>>> MyParser().feed('&gt; &#62; &#x3E;')
62
x3E

I've seen code in the wild doing unichr(int(data)) in handle_charref (once they figured out that '62' is passed) and then fail when an hex entity is found.  Passing 'x3E' doesn't seem too useful because the user has to first check if there's a leading 'x', if there is remove it, then convert the hex string to int, and finally use unichr() to get the char, otherwise just convert to int and use unichr().

There 3 different possible solutions:
1) just document the behavior;
2) normalize the hex value before passing them to handle_charref and document it;
3) add a new handle_entity method that is called with the character represented by the entity (named, decimal, or hex);

The first solution alone doesn't solve much, but the doc should be clearer regardless of the decision we take.
The second one is better, but if it's implemented there won't be any way to know if the entity had a decimal or hex value anymore (does anyone care?).  The normalization should also convert the hex string to int and then convert it back to str to be consistent with decimal entities.
The third one might be better, but doesn't solve the issue on 2.7/3.2.  People don't care about entities and just want the equivalent char, so having a method that converts them already sounds like a useful feature to me.

----------
assignee: ezio.melotti
components: Library (Lib)
messages: 149822
nosy: eric.araujo, ezio.melotti
priority: normal
severity: normal
stage: test needed
status: open
title: Handling of hex character references in HTMLParser.handle_charref
type: enhancement
versions: Python 2.7, Python 3.2, Python 3.3

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Python tracker <report at bugs.python.org>
<http://bugs.python.org/issue13633>
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