regular expression: how to fail on double characters?

say i have 'hello'
and i want to it to fail when it matches double l, (2 or more actually).

any ideas?

import re
str1 = "this is crazy"
str2 = "thiis is crazy"
if re.search('i{2,}',str1) is not None: print "first"
if re.search('i{2,}',str2) is not None: print "second"


the '{a,b}' specifies it is looking for between a and b occurences of it. If you leave out the b, it looks for minimum of a occurneces. Similarly with leaving out the a

Lazy's regex will work fine, but it requires that you know what letter will occure twice (or more) before hand.. which can be very restricting! lucky you can match any letter occuring twice using backreferances with no more effort ..

This small Python shell session should work:

>>> import re
>>> string = 'hello'
>>> re.search('([a-z])\\1', string.lower()) != None
True
>>> string = 'hi there'
>>> re.search('([a-z])\\1', string.lower()) != None
False
>>>

Note: because of the lower() method this is effectivly a case insentative match.

Mark.