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In Python 3.2b2, html.entities.codepoint2name and name2codepoint only support the 252 HTML entity names defined in the HTML 4 spec from 1997. I'm wondering if there's a reason not to support W3C Recommendation 'XML Entity Definitions for Characters' 
http://www.w3.org/TR/xml-entity-names/
This standard contains significantly more characters, and it is noted in that spec that the HTML 5 drafts use that spec's entities. You can see the current HTML 5 'Named character references' here: 
http://www.w3.org/TR/html5/named-character-references.html#named-character-references
If this is just a matter of somebody going in to do the grunt work, let me know. 
If startup costs associated with importing a huge dictionary are a concern, perhaps a more efficient type that enables the same lookup interface can be defined. 
If other reasons exist to not move in this direction, please do let me know!

Supporting the ones in HTML 5 would be fine with me. Supporting those of xml-entity-names would be inappropriate - it's not clear (to me, at least) that all of them are really meant for use in HTML.

Agreed with Martin. I wonder if we should provide a means to use only HTML 4.01 entity references (say with a function parameter html5 defaulting to True) or we should just update the mapping.

I don't see the need for a parameter to support different sets of entities. Just supporting the ones from HTML 5 seems like the right thing.

To make my intent explicit: an updated mapping could generate references invalid for 4.01.

Ah. I hadn't thought of generating them, only parsing them. In that case, then yes, it's an issue for generation.

I just closed #12329 as a duplicate of this bug. It requested the addition of the apos named entity reference.
TTBOMK, the html module (or htmlentitydefs in 2.x) doesn’t claim to support XHTML TTBOMK; an XML parser should be used for XHTML. In HTML 4.01, apos is not defined, but it is in HTML5.

The reason I raised #12329 was that the v2.7.1 documentation in
http://docs.python.org/library/htmllib.html#module-htmlentitydefs
says:
"... The definition provided here contains all the entities defined by XHTML 1.0 ..."
The only diff between the 252 HTML 4.01 and 253 XHTML 1.0 entities is "apos". See http://www.w3.org/TR/html401/sgml/entities.html and http://www.w3.org/TR/xhtml1/dtds.html .

BTW, the HTMLParser module (as well as html.parser in 3.x) does claim to parse both HTML and XHTML, see http://docs.python.org/library/htmlparser.html#module-HTMLParser .

Ah, this changes the situation. I suppose it’s too late to stop pretending that HTML and XHTML are nearly the same thing (IOW change the doc), so apos needs to be defined for XHTML.
IMO, we need a way to have the right entity references for HTML 4.01, XHTML 1.0 and HTML5, not put them all in one mapping.

Having them in different mappings would be good, but I expect that for most real world application a single mappings that includes them all is the way to go. If I'm parsing a supposedly HTML page that contains an ' I'd rather have it converted even if it's not an HTML entity.
If the set of entities supported by HTML5 is a superset of the HTML4 and XHTML ones, than we might just use that (I haven't checked though).

http://www.w3.org/TR/html5/named-character-references.html lists 2152 HTML 5 entities (see also attached file for a dict generated from that table).
Currently html.entities only has 252 entities, organized in 3 dicts:
 1) name -> intvalue (e.g. 'amp': 0x0026);
 2) intvalue -> name (e.g. 0x0026: 'amp');
 3) name -> char (e.g. 'amp': '&');
In HTML 5, some of the entities map to a sequence of 2 characters, for example ≂̸ corresponds to [U+2242, U+0338] (i.e. MINUS TILDE + COMBINING LONG SOLIDUS OVERLAY).
This means that:
 1) the current approach of having a dict with name -> intvalue doesn't work anymore, and a name -> valuelist should be used instead;
 2) the reverse dict for this would have to use tuples as keys, but I'm not sure how useful would that be (producing entities is not a common case, especially "unusual" ones like these).
 3) The name -> char dict might still be useful, and can easily become a name -> str dict in order to deal with the multichar entities;
Since 1) is not backward-compatible the HTML5 entities should probably go in a separate dict.
Also note that the entities are case-sensitive and some of them include different spellings (e.g. both 'amp' and 'AMP' map to '&'), so the reverse dict won't work too well. Having '&' -> 'amp' seems better than '&' -> 'AMP', but this might not be obvious for all the entities and requires some extra logic in the code to get it right.

> 1) the current approach of having a dict with name -> intvalue doesn't work anymore, and a name -> valuelist should be used instead;
> 2) the reverse dict for this would have to use tuples as keys, but I'm not sure how useful would that be (producing entities is not a common case, especially "unusual" ones like these).
> 3) The name -> char dict might still be useful, and can easily become a name -> str dict in order to deal with the multichar entities;
> 
> Since 1) is not backward-compatible the HTML5 entities should probably go in a separate dict.
+1 for a separate dict; -1 for a value list. The right value type is
'str'; name2codepoint ought to be deprecated (it's a left-over from
when the str type wasn't unicode in 2.x).
As for the reverse mapping: I'd add a dictionary that is reverse to
entitydefs (i.e. with str keys). That some keys then have two characters
is no real issue: applications that want to use this dictionary can
either ignore them, or follow the approach of always checking
Unicode combining characters - I'd expect that all "second" characters
are indeed combining.
OTOH, it's easy enough to create an inverted dictionary yourself
when you need it, and not every three-line function needs to be
in the standard library. It might actually be more useful to compile
the values into a regular expression which you can then use to
find out whether characters can be escaped using entity references.

Attached another file with a dict that contains the 2231 HTML5 entities listed at http://www.w3.org/TR/html5/named-character-references.html
The dict is like:
html5namedcharref = {
 'Aacute;': '\xc1',
 'Aacute': '\xc1',
 'aacute;': '\xe1',
 'aacute': '\xe1',
 'Abreve;': '\u0102',
 'abreve;': '\u0103',
 ...
}
A better name could be found for the dict if you have better ideas (maybe html.entities.html5 only?). The dict will be added to html.entities.

Here is a proper patch, still using the html5namedcharref name.
HTMLParser should also be updated to use this dict.

How about calling it just "html5", or "HTML5"? That it is about entities already follows from the module name.

Here's a new patch that uses the "html5" name for the dict, if there aren't other comments I'll commit it.

New changeset 2b54e25d6ecb by Ezio Melotti in branch 'default':
#11113: add a new "html5" dictionary containing the named character references defined by the HTML5 standard and the equivalent Unicode character(s) to the html.entities module.
http://hg.python.org/cpython/rev/2b54e25d6ecb 

The ';' is not part of the entity name but an SGML delimiter, like '&'; the strings in the dict should not include it (like in the other dict they don’t).

BTW in the doc you may point to collections.ChainMap to explain to people how to make one dict with HTML 4 and HTML 5 entities. (Note that I assume there are two dicts, but I only skimmed the diff.)

The problem is that the standard allows some charref to end without a ';', but not all of them.
So both "&Eacuteric" and Éric" will be parsed as "Éric", but only "αcentauri" will result in "αcentauri" -- "&alphacentauri" will be returned unchanged.
I'm now working on #15156 to use this dict in HTMLParser, and detecting the ';'-less entities is not easy. A possible solution is to keep the names that are accepted without ',' in a separate (private) dict and expose a function like HTMLParser.unescape that implements all the necessary logic.
Regarding ChainMap, the html5 dict should be a superset of the html4 one.

The explanations make sense, don’t change anything.