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On 15May2019 23:06, [email protected] <[email protected]> wrote:
>I'm no regex-crack; when I want to extract a string from HTML-Source, I
>usually do something like:
>
> class=(["\'])title\1.+?>(.+?)<
>
>In an example from "real programmers" I found (look at the part after "\1"):
>
> class=(["\'])title\1[^>]*>([^<]+)
>
>Is there a significant advantage of this example?
Well, the latter one only collects up to the start of the closing tag.
The former seems to consume the "<" of the closing tag.
However, they're both a bit deficient. The former doesn't expect
anything in the opening tag after the class= - it would consider a
quoted closing > to end the tag, eg:
<a class="title" href="blah>blah">...
to end at "blah>".
The latter doesn't match such a tag at all - it expects there to be _no_
attributes after class=. And it ends prematurely at the same point with
the example tag above.
I tend to use the latter construction: ([^>]*)
(Hey, the string might be empty!) But I pretty much never use the
nongreedy stuff - lack of practice and of course there are regexp
flavours where they're not supported.
However, why not just use a proper HTML parser? You need a correct
implementation of the grammar to be robust. I've written regexp based
HTML parsers in the past. Jeez. They're cumbersome and slow.
You could switch languages and use a third party library. The common
example is Python and BeautifulSoup. Then all you need to do is select
tags with a "title" class and get their text component.
Cheers,
Cameron Simpson <[email protected]>
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<p>On 15May2019 23:06, [email protected] <[email protected]> wrote:<br>
>I'm no regex-crack; when I want to extract a string from HTML-Source, I <br>
>usually do something like:<br>
><br>
> class=(["\'])title\1.+?>(.+?)<<br>
><br>
>In an example from "real programmers" I found (look at the part after "\1"):<br>
><br>
> class=(["\'])title\1[^>]*>([^<]+)<br>
><br>
>Is there a significant advantage of this example?<br>
<br>
Well, the latter one only collects up to the start of the closing tag. <br>
The former seems to consume the "<" of the closing tag.<br>
<br>
However, they're both a bit deficient. The former doesn't expect <br>
anything in the opening tag after the class= - it would consider a <br>
quoted closing > to end the tag, eg:<br>
<br>
<a class="title" href="blah>blah">...<br>
<br>
to end at "blah>".<br>
<br>
The latter doesn't match such a tag at all - it expects there to be _no_ <br>
attributes after class=. And it ends prematurely at the same point with <br>
the example tag above.<br>
<br>
I tend to use the latter construction: ([^>]*)<br>
(Hey, the string might be empty!) But I pretty much never use the <br>
nongreedy stuff - lack of practice and of course there are regexp <br>
flavours where they're not supported.<br>
<br>
However, why not just use a proper HTML parser? You need a correct <br>
implementation of the grammar to be robust. I've written regexp based <br>
HTML parsers in the past. Jeez. They're cumbersome and slow.<br>
<br>
You could switch languages and use a third party library. The common <br>
example is Python and BeautifulSoup. Then all you need to do is select <br>
tags with a "title" class and get their text component.<br>
<br>
Cheers,<br>
Cameron Simpson <[email protected]><br>
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