Extracting "true" words

[candide]

Back again with my study of regular expressions ;) There exists a
special character allowing alphanumeric extraction, the special
character \w (BTW, what the letter 'w' refers to?). But this feature
doesn't permit to extract true words; by "true" I mean word composed
only of _alphabetic_ letters (not digit nor underscore).

So I was wondering what is the pattern to extract (or to match) _true_
words ? Of course, I don't restrict myself to the ascii universe so that
the pattern [a-zA-Z]+ doesn't meet my needs.

[Chris Rebert]

On Fri, Apr 1, 2011 at 1:55 PM, candide <can...@free.invalid> wrote:
> Back again with my study of regular expressions ;) There exists a special
> character allowing alphanumeric extraction, the special character \w (BTW,
> what the letter 'w' refers to?).

"Word" presumably/intuitively; hence the non-standard "[:word:]"
POSIX-like character class alias for \w in some environments.

> But this feature doesn't permit to extract
> true words; by "true" I mean word composed only of _alphabetic_ letters (not
> digit nor underscore).

Are you intentionally excluding CJK ideographs (as not "letters"/alphabetic)?
And what of hyphenated terms (e.g. "re-lock")?

> So I was wondering what is the pattern to extract (or to match) _true_ words
> ? Of course, I don't restrict myself to the ascii universe so that the
> pattern [a-zA-Z]+ doesn't meet my needs.

AFAICT, there doesn't appear to be a nice way to do this in Python
using the std lib `re` module, but I'm not a regex guru.
POSIX character classes are unsupported, which rules out "[:alpha:]".
\w can be made Unicode/locale-sensitive, but includes digits and the
underscore, as you've already pointed out.
\p (Unicode property/block testing), which would allow for
"\p{Alphabetic}" or similar, is likewise unsupported.

Cheers,
Chris
--
http://blog.rebertia.com

[MRAB]

On 01/04/2011 21:55, candide wrote:
> Back again with my study of regular expressions ;) There exists a
> special character allowing alphanumeric extraction, the special
> character \w (BTW, what the letter 'w' refers to?). But this feature
> doesn't permit to extract true words; by "true" I mean word composed
> only of _alphabetic_ letters (not digit nor underscore).
>

The 'w' refers to a 'word' character, although in regex it refers to
letters, digits and the underscore character '_' due to its use in
computer languages (basically, the characters of an identifier or name).

>
> So I was wondering what is the pattern to extract (or to match) _true_
> words ? Of course, I don't restrict myself to the ascii universe so that
> the pattern [a-zA-Z]+ doesn't meet my needs.
>

Using the re module, you would have to create a character class out of
all the possible letters, something like this:

letter_class = u"[" + u"".join(unichr(c) for c in range(0x10000) if
unichr(c).isalpha()) + u"]"

Alternatively, you could try the new regex implementation here:

http://pypi.python.org/pypi/regex

which adds support for Unicode properties, and do something like this:

words = regex.findall(ur"\p{Letter}+", unicode_text)

[John Nagle]

On 4/1/2011 4:10 PM, Chris Rebert wrote:
> On Fri, Apr 1, 2011 at 1:55 PM, candide<can...@free.invalid> wrote:
>> Back again with my study of regular expressions ;) There exists a special
>> character allowing alphanumeric extraction, the special character \w (BTW,
>> what the letter 'w' refers to?).
>
> "Word" presumably/intuitively; hence the non-standard "[:word:]"
> POSIX-like character class alias for \w in some environments.
>
>> But this feature doesn't permit to extract
>> true words; by "true" I mean word composed only of _alphabetic_ letters (not
>> digit nor underscore).
>
> Are you intentionally excluding CJK ideographs (as not "letters"/alphabetic)?
> And what of hyphenated terms (e.g. "re-lock")?

It's an interesting parsing problem to find word breaks in mixed
language text. It's quite common to find English and Japanese text
mixed. (See "http://www.dokidoki6.com/00_index1.html". Caution,
excessively cute.) Each ideograph is a "word", of course.

Parse this into words:

★12/25/2009★
6%DOKIDOKI VISUAL FILE vol.4を公開しました。
アルバムの上部で再生操作、下部でサムネイルがご覧いただけます。

John Nagle

[candide]

Le 02/04/2011 01:10, Chris Rebert a écrit :

> "Word" presumably/intuitively; hence the non-standard "[:word:]"
> POSIX-like character class alias for \w in some environments.

OK

> Are you intentionally excluding CJK ideographs (as not "letters"/alphabetic)?

Yes, CJK ideographs don't belong to the locale I'm working with ;)

> And what of hyphenated terms (e.g. "re-lock")?

I'm interested only with ascii letters and ascii letters with diacritics

Thanks for your response.