N00b question: matching stuff with variables.
in [Python]
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From: Ken D'Ambrosio on 28 Jun 2010 13:29 Hi, all. I've got a file which, in turn, contains a couple thousand filenames. I'm writing a web front-end, and I want to return all the filenames that match a user-input value. In Perl, this would be something like, if (/$value/){print "$_ matches\n";} But trying to put a variable into regex in Python is challenging me -- and, indeed, I've seen a bit of scorn cast upon those who would do so in my Google searches ("You come from Perl, don't you?"). Here's what I've got (in ugly, prototype-type code): file=open('/tmp/event_logs_listing.txt' 'r') # List of filenames seek = form["serial"].value # Value from web form for line in file: match = re.search((seek)",(.*),(.*)", line) # Stuck here Clearly, the line, above, is just plain ol' wrong, but I'm including it to give a hint of what I'm trying to do. What's the correct Python-esque way to go about this? Thanks! -Ken -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.
From: Thomas Jollans on 28 Jun 2010 13:46 On 06/28/2010 07:29 PM, Ken D'Ambrosio wrote: > Hi, all. I've got a file which, in turn, contains a couple thousand > filenames. I'm writing a web front-end, and I want to return all the > filenames that match a user-input value. In Perl, this would be something > like, > > if (/$value/){print "$_ matches\n";} > > But trying to put a variable into regex in Python is challenging me -- > and, indeed, I've seen a bit of scorn cast upon those who would do so in > my Google searches ("You come from Perl, don't you?"). > > Here's what I've got (in ugly, prototype-type code): > > file=open('/tmp/event_logs_listing.txt' 'r') # List of filenames > seek = form["serial"].value # Value from web form > for line in file: > match = re.search((seek)",(.*),(.*)", line) # Stuck here without re: for line in file: if line.startswith(seek): # or: if seek in line... # do stuff with re and classic string formatting: for line in file: # or use re.match to look only at the beginning of the line match = re.search('(%s),(.*),(.*)' % seek, line) if match: #use match.group(n) for further processing You could also concatenate strings to get the regexp, as in: '('+seek+'),(.*),(.*)' Note that while using re is perl way to do strings, Python has a bunch of string methods that are often a better choice, such as str.startswith or the ("xyz" in "vwxyz!") syntax. if you just want to get the matching lines, you could use list comprehension: matching = [ln for ln in file if ln.startswith(seek)] Just to present some of the ways you can do this in Python. I hope you're enjoying the language. -- Thomas
From: Stephen Hansen on 28 Jun 2010 13:49 On 6/28/10 10:29 AM, Ken D'Ambrosio wrote: > Hi, all. I've got a file which, in turn, contains a couple thousand > filenames. I'm writing a web front-end, and I want to return all the > filenames that match a user-input value. In Perl, this would be something > like, > > if (/$value/){print "$_ matches\n";} > > But trying to put a variable into regex in Python is challenging me -- > and, indeed, I've seen a bit of scorn cast upon those who would do so in > my Google searches ("You come from Perl, don't you?"). First of all, if you're doing this, you have to be aware that it is *very* possible to write a pathological regular expression which will can kill your app and maybe your web server. So if you're letting them write regular expressions and they aren't like, smartly-trusted-people, be wary. > Here's what I've got (in ugly, prototype-type code): > > file=open('/tmp/event_logs_listing.txt' 'r') # List of filenames > seek = form["serial"].value # Value from web form > for line in file: > match = re.search((seek)",(.*),(.*)", line) # Stuck here Now, if you don't need the full power of regular expressions, then what about: name, foo, bar = line.split(",") if seek in name: # do something with foo and bar That'll return True if the word 'seek' appears in the first field of what appears to be the comma-delimited line. Or maybe, if you're worried about case sensitivity: if seek.lower() in name.lower(): # la la la You can do a lot without ever bothering to mess around with regular expressions. A lot. Its also faster if you're doing simpler things :) If they don't need to do the full power of regular expressions, but just simple globbing? Then maybe change it to: seeking = re.escape(seek) seeking = seeking.replace("\\*", ".*") seeking = seeking.replace("\\?", ".") match = re.search(seeking + ",(.*),(.*)", line) FIrst, we escape the user input so they can't put in any crazy regular expression characters. Then we go and *unescape* "\\*" and turn it into a ".*" -- becaues when a user enters "*", the really mean ".*" in traditional glob-esque. Then we do the same with the question mark turning into a dot. Then! We go and run our highly restricted regular expression through basically just as you were doing before-- you just didn't concatenate the 'seek' string to the rest of your expression. If you must give them full regex power and you know they won't try to bomb you, just leave out the 'seeking = ' lines and cross your fingers. -- ... Stephen Hansen ... Also: Ixokai ... Mail: me+list/python (AT) ixokai (DOT) io ... Blog: http://meh.ixokai.io/
From: Rami Chowdhury on 28 Jun 2010 13:55 On Monday 28 June 2010 10:29:35 Ken D'Ambrosio wrote: > Hi, all. I've got a file which, in turn, contains a couple thousand > filenames. I'm writing a web front-end, and I want to return all the > filenames that match a user-input value. In Perl, this would be something > like, > > if (/$value/){print "$_ matches\n";} I presume you're suitably sanitizing $value before you arbitrarily use it ;-)? > file=open('/tmp/event_logs_listing.txt' 'r') # List of filenames > seek = form["serial"].value # Value from web form > for line in file: > match = re.search((seek)",(.*),(.*)", line) # Stuck here Not sure what you're trying to do, here, with the extra regex groups? If you just want to naively check for the presence of that user-input value, you can do: seek = sanitize(form["serial"].value) for line in file: match = re.search(seek, line) # re.search(pattern, string, flags) if match is not None: print "%s matches" % line One thing that certainly confused me when I learned Python (coming from, among other things, Perl) was the lack of implicit variables -- is that what's tripping you up? Hope that helps, Rami ---- Rami Chowdhury "Given enough eyeballs, all bugs are shallow." -- Linus' Law +1-408-597-7068 / +44-7875-841-046 / +88-01819-245544
From: Sion Arrowsmith on 29 Jun 2010 05:51
Stephen Hansen <me+list/python(a)ixokai.io> wrote: >On 6/28/10 10:29 AM, Ken D'Ambrosio wrote: >> for line in file: >> match = re.search((seek)",(.*),(.*)", line) # Stuck here > [ ... ] > name, foo, bar = line.split(",") > if seek in name: > # do something with foo and bar > >That'll return True if the word 'seek' appears in the first field of >what appears to be the comma-delimited line. If the file input is comma-delimited, then the OP might very well want a look at the csv module. Something like: for line in reader(file): if line[0] == seek: # first field matches, do something with line[-1] and line[-2] # -- I'm not quite sure what the semantics of a pair of greedy # (.*)s would be -- \S under construction |