How to print all expressions that match a regular expression
in [Python]
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From: hzhuo1 on 6 Feb 2010 14:36 Hi, I am a fresh man with python. I know there is regular expressions in Python. What I need is that given a particular regular expression, output all the matches. For example, given [1|2|3]{2} as the regular expression, the program should output all 9 matches, i.e., "11 12 13 21 22 23 31 32 33". Is there any well-written routine in Python or third-party program to do this? If there isn't, could somebody make some suggestions on how to write it myself? Thanks. Zhuo
From: Roy Smith on 6 Feb 2010 17:23 In article <ee2cfd35-3171-4ee7-ad3a-cf117e5527c5(a)r24g2000yqd.googlegroups.com>, "hzhuo1(a)gmail.com" <hzhuo1(a)gmail.com> wrote: > Hi, > > I am a fresh man with python. I know there is regular expressions in > Python. What I need is that given a particular regular expression, > output all the matches. For example, given �[1|2|3]{2}� as the regular > expression, the program should output all 9 matches, i.e., "11 12 13 > 21 22 23 31 32 33". > > Is there any well-written routine in Python or third-party program to > do this? If there isn't, could somebody make some suggestions on how > to write it myself? > > Thanks. > > Zhuo Please enumerate all the strings which match ".*". Use additional sheets of paper if needed.
From: Ben Finney on 6 Feb 2010 17:43 Roy Smith <roy(a)panix.com> writes: > "hzhuo1(a)gmail.com" <hzhuo1(a)gmail.com> wrote: > > What I need is that given a particular regular expression, output > > all the matches. […] > Please enumerate all the strings which match ".*". Use additional > sheets of paper if needed. +1 QOTW -- \ “Are you pondering what I'm pondering?” “I think so, ... Brain, | `\ but how can we get seven dwarves to shave their legs?” —_Pinky | _o__) and The Brain_ | Ben Finney
From: hzhuo1 on 6 Feb 2010 19:05 Thanks for your reply. So there isn't such a routine just because some of the regular expressions cannot be enumerated. However, some of them can be enumerated. I guess I have to write a function myself. Zhuo On Feb 6, 5:23 pm, Roy Smith <r...(a)panix.com> wrote: > In article > <ee2cfd35-3171-4ee7-ad3a-cf117e552...(a)r24g2000yqd.googlegroups.com>, > > > > > > "hzh...(a)gmail.com" <hzh...(a)gmail.com> wrote: > > Hi, > > > I am a fresh man with python. I know there is regular expressions in > > Python. What I need is that given a particular regular expression, > > output all the matches. For example, given ³[1|2|3]{2}² as the regular > > expression, the program should output all 9 matches, i.e., "11 12 13 > > 21 22 23 31 32 33". > > > Is there any well-written routine in Python or third-party program to > > do this? If there isn't, could somebody make some suggestions on how > > to write it myself? > > > Thanks. > > > Zhuo > > Please enumerate all the strings which match ".*". Use additional sheets > of paper if needed.
From: Steven D'Aprano on 6 Feb 2010 19:26
On Sat, 06 Feb 2010 16:05:15 -0800, hzhuo1(a)gmail.com wrote: > Thanks for your reply. > So there isn't such a routine just because some of the regular > expressions cannot be enumerated. However, some of them can be > enumerated. I guess I have to write a function myself. How do you expect to tell the ones that can be enumerated apart from those that can't be? Regular expressions are programs in a "regex" programming language. What you are asking for is the same as saying: "Is there a program that can enumerate every possible set of data that is usable as valid input for a given program?" This, in turn, is equivalent to the Halting Problem -- if you can solve one, you can solve the other. You might like to google on the Halting Problem before you spend too much time on this. (Note, however, it isn't necessary to solve the Halting Problem for *all* cases in order to have a useful Endless Loop Detector program.) Why do you think you need this? Seems to me you're starting on an extraordinarily difficult job. I hope the benefit is equally extraordinary. [Aside: Python regexes aren't Turing Complete. I'm not sure about Perl regexes. Either way, this might actually be less difficult than the Halting Problem, as in "amazingly difficult" rather than "impossible".] -- Steven |