On Apr 24, 1:29 am, Piet van Oostrum <p...@cs.uu.nl> wrote: > >>>>> John Machin <sjmac...@lexicon.net> (JM) wrote: > >JM> On Apr 23, 8:01 am, krishnaposti...@gmail.com wrote: > >>> Requirements: > >>> The text must contain a combination of numbers, alphabets and hyphen > >>> with at least two of the three elements present. > >JM> Unfortunately(?), regular expressions can't express complicated > >JM> conditions like that. > > Yes, they can but it is not pretty. > > The pattern must start with a letter, a digit or a hyphen. > > If it starts with a letter, for example, there must be at least a hyphen > or a digit somewhere. So let us concentrate on the first one of these > that occurs in the string. Then the preceding things are only letters > and after it can be any combination of letters, digits and hyphens. So > the pattern for this is (when we write L for letters, and d for digits): > > L+[-d][-Ld]*. > > Similarly for strings starting with a digit and with a hyphen. Now > replacing L with [A-Za-z] and d with [0-9] or \d and factoring out the > [-Ld]* which is common to all 3 cases you get: > > (?:[A-Za-z]+[-0-9]|[0-9]+[-A-Za-z]|-+[0-9A-Za-z])[-0-9A-Za-z]* > > >>> obj = > >>> re.compile(r'(?:[A-Za-z]+[-0-9]|[0-9]+[-A-Za-z]|-+[0-9A-Za-z])[-0-9A-Za-z]*') > >>> re.findall(obj, 'TestThis;1234;Test123AB-x') > > ['Test123AB-x'] > > Or you can use re.I and mention only one case of letters: > > obj = re.compile(r'(?:[a-z]+[-0-9]|[0-9]+[-a-z]|-+[0-9a-z])[-0-9a-z]*', re.I)
Understandable and maintainable, I don't think. Suppose that instead the first character is limited to being alphabetic. You have to go through the whole process of elaborating the possibilites again, and I don't consider that process qualifies as "express[ing] complicated conditions like that". -- http://mail.python.org/mailman/listinfo/python-list
