This is something very useful which I picked up from a mailing list, so I’m certainly not claiming to have come up with it.
The problem: basically, you need to replace some text or code using a regular expression in Python, but you need that regular expression to contain a variable reference so it can be run within a loop etc. How do you do this?
The example below is the actual one I was working on — I needed to replace a <div> tag with a changing id with the actual contents of a file within Zope, in order to insert HTML snippets (YouTube video, Google code etc.) into a page. The page editing tool we use (EditonPro) sensibly strips out this kind of stuff, but this was a special case where the site editor really needed to do this. The inserted tags looked something like this:
<div id="snippet-123456">
[snippet: YouTube video of something]
</div>
Then I defined a method (getSnippet.py) with the following code:
import re
def getSnippet(self, content):
content = content.replace('\n','')
pattern = re.compile(r"""(<div id="snippet
-)([^"]*)(">[^<]*)(</div>)""", re.MULTILINE)
reg = re.findall(pattern, content)
if reg:
count = len(reg)
i=0
while i < count:
snpid = str(reg[i][1])
sr = r"""<div id="snippet-%s"[^<]*</div>"""
src = re.compile(sr % snpid)
srch = src.findall(content)
srch = srch[0]
try:
repl = self.aq_parent[snpid].data
except:
repl = ''
content = content.replace(srch, repl)
i=i+1
return content
Briefly, this is how this works: in the document_view page template a call is made to getSnippet thus:
<div tal:define="content here/CookedBody"
tal:replace="structure python: here.getSnippet(content)"/>
The page content is passed to the getSnippet External Method which first does a regex to find all the relevant bits of code. If anything is returned in the variable “reg”, a while loop is initiated.
The div ids, which map to file names of the Zope files, are extracted from “reg” while this loop runs. We use them to construct a regular expression which will match the relevant snippet code. The key lines are these:
sr = r"""<div id="snippet-%s"[^<]*</div>"""
src = re.compile(sr % snpid)
We use the %s syntax when defining our regular expression and pass the variable to it when compiling it.
It works, great stuff.