Vamsee Krishna Gomatam wrote:
> Hello,
> I'm having some problems understanding Regexps in Python. I want
> to replace "<google>PHRASE</google>" with
> "<a href=http://www.google.com/search?q=PHRASE>PHRASE</a>" in a block of
> text. How can I achieve this in Python? Sorry for the naive question but
> the documentation is really bad :-(
VKG,
Sorry you had such difficulty; if you can explain in a bit more detail,
we could perhaps fix that "really bad" [compared with what?] documentation.
Whether you are doing a substitution programatically in Python, or in
any other language, or manually using a text editor, you need to specify
some input text, a pattern, and a replacement.
The syntax for pattern and replacement for what you want to do differs
in only minor details (if at all) among major languages and common text
editors, and it's been that way for years. For example, see the
retro-computing museum exhibit at the end of this posting.
So, did you have any problem determining that PHRASE is represented by
(.*) -- good enough if there is only one occurrence of your target -- in
the pattern, and by \1 in the replacement?
Did you have a problem with this part of the docs (which is closely
followed by an example with \1 in the replacement), and if so, what was
the problem?
sub( pattern, repl, string[, count])
Return the string obtained by replacing the leftmost non-overlapping
occurrences of pattern in string by the replacement repl.
Have you used regular expressions before? If not, then you shouldn't
expect to learn how to use them from the documentation, which does
adequately _document_ the provided functionality. This is just like how
the manual supplied with a new car documents the car's functionality,
but doesn't attempt to teach how to drive it. If you haven't done so
already, you may like to do what the documentation suggests:
consult the Regular Expression HOWTO, accessible from
http://www.python.org/doc/howto/.
And out with the magic lantern ... here's the promised blast from the
past, using Oliver's sample input:
C:\junk>dir \bin\ed.com
[snip]
30/11/1985 04:43p 18,936 ed.com
[snip]
C:\junk>ed
Memory available : 59K bytes
>a
This is a <google>Python</google>. And some randomnonsense test.....
.
>p
This is a <google>Python</google>. And some randomnonsense test.....
>s/<google>\(.*\)<\/google>/<a
href=http:\/\/www.google.com\/search?q=\1>\1<\/a>/
>p
This is a <a href=http://www.google.com/search?q=Python>Python</a>. And
some randomnonsense test.....
>
Cheers,
John
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