Revision 12 as of 2006-01-28 11:19:02

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Reference Diagrams

http://taoriver.net/img/for_pi/regex_characters.png

flags when compiling:

http://taoriver.net/img/for_pi/regex_flags.png

(All images PD, released by me, author, LionKimbro.)

DavidMertz has also created [http://gnosis.cx/TPiP/regex_patterns.gif a regular expression reference.]

Searching & Matching

You can search or match.

You can also split on a pattern.

For example:

   1 import re
   2 split_up = re.split(r"(\(\([^)]+\)\))",
   3                     "This is a ((test)) of the ((emergency broadcasting station.))")

...which produces:

["This is a ", "((test))", " of the ", "((emergency broadcasting station.))" ]

Compiling

If you use a regex a lot, compile it first.

Consider:

   1 import re
   2 match_obj=re.match("<(.*?)>(.*?)</(.*?)>", "<h1>robot</h1>")
   3 print mo.groups()

...which outputs: ('h1', 'robot', 'h1')

If you were going to do that match a lot, you could compile it, like so:

   1 import re
   2 match_re=re.compile("<(.*?)>(.*?)</(.*?)>")
   3 match_obj=match_re.match("<h1>robot</h1>")
   4 print match_obj.groups()

...which yields the same result.

I don't know how much faster compiled forms are than non-compiled forms.

Links

For those interested in visualization, you may also be interested in a [http://www.ozonehouse.com/mark/blog/code/PeriodicTable.pdf periodic table of PERL operators.]

Missing unicode documentation

Any documentation is misisng on how to use re with unicode on python http://www.amk.ca/python/howto/regex/

Missing features

The following feature does not seems to work in python:

For example, the ICU regular expression provides the following patterns:

Discussion

I've made a couple of diagrams, which I've linked at the top of the page here.

I have SVG links as well; [http://taoriver.net/img/for_pi/regex_characters.svg first] and [http://taoriver.net/img/for_pi/regex_flags.svg second.]

Damn the [http://visual.wiki.taoriver.net/moin.cgi/LongImageIncorporationProcess LongImageIncorporationProcess!] Damn it to hell! We'd have a billion pretty pictures here, if tablets were cheap, and we had protocols and implementations for saving and loading straight to and from the wiki.

I have another diagram I'd like to make and place; It's the pattern (RegexObject) and match (MatchObject) API, visualized, and arranged dense. We'll see if I get around to drawing it, but it looks like no. Too much else to do.

-- LionKimbro DateTime(2004-12-28T08:38:12Z)

The image isn't meant to be explanatory, it is meant to be reference and refreshing material.

That said: The "match string" is the final product of either of the two above expressions. It is what the above two expressions will literally match. If you have a better phrase, or would like to correct "raw" to "regex," feel free to download the SVG, edit the text, place an image on the web, and link it from here. (The damn [http://visual.wiki.taoriver.net/moin.cgi/LongImageIncorporationProcess LongImageIncorporationProcess] strikes again.) I may eventually get around to it myself one day, but it seems there are higher priorities, and the diagram is "good enough."

That said, I appreciate the correction. -- LionKimbro DateTime(2005-01-01T00:22:14Z)

I should mention: PythonCard comes with "redemo," which is simply indispensible if you are doing a bunch of regex work.

It lets you type in a regular expression, and highlights matches. You can edit either regex or text, the highlights adjust in realtime. And then, it prints out how the .groups() are identified in code. It's terribly useful. -- LionKimbro DateTime(2005-07-19T23:34:53Z)

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