Regular Expressions: Can't quite figure this problem out
Gabriel Genellina
gagsl-py2 at yahoo.com.ar
Tue Sep 25 00:23:30 EDT 2007
En Mon, 24 Sep 2007 23:51:57 -0300, Robert Dailey <rcdailey at gmail.com>
escribi�:
> What I meant was that it's not an option because I'm trying to learn
> regular
> expressions. RE is just as built in as anything else.
Ok, let's analyze what you want. You have for instance this text:
"<action></action>"
which should become
"<action/>"
You have to match:
(opening angle bracket)(any word)(closing angle bracket)(opening angle
bracket)(slash)(same word as before)(closing angle bracket)
This translates rather directly into this regular expression:
r"<(\w+)></\1>"
where \w+ means "one or more alphanumeric characters or _", and being
surrounded in () creates a group (group number one), which is
back-referenced as \1 to express "same word as before"
The matched text should be replaced by (opening <)(the word
found)(slash)(closing >), that is: r"<\1/>"
Using the sub function in module re:
py> import re
py> source = """
... <root></root>
... <root/>
... <root><frame type="image"><action></action></frame></root>
... <root><frame type="image"><action/></frame></root>
... """
py> print re.sub(r"<(\w+)></\1>", r"<\1/>", source)
<root/>
<root/>
<root><frame type="image"><action/></frame></root>
<root><frame type="image"><action/></frame></root>
Now, a more complex example, involving tags with attributes:
<frame type="image"></frame> --> <frame type="image" />
You have to match:
(opening angle bracket)(any word)(any sequence of words,spaces,other
symbols,but NOT a closing angle bracket)(closing angle bracket)(opening
angle bracket)(slash)(same word as before)(closing angle bracket)
r"<(\w+)([^>]*)></\1>"
[^>] means "anything but a >", the * means "may occur many times, maybe
zero", and it's enclosed in () to create group 2.
py> source = """
... <root></root>
... <root><frame type="image"></frame></root>
... """
py> print re.sub(r"<(\w+)([^>]*)></\1>", r"<\1\2 />", source)
<root />
<root><frame type="image" /></root>
Next step would be to allow whitespace wherever it is legal to appear -
left as an exercise to the reader. Hint: use \s*
--
Gabriel Genellina
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