trying to match a string

[Andrew Freeman]

Andrew Freeman wrote:
> oj wrote:
>> On Jul 18, 12:10 pm, John Machin <sjmac... at lexicon.net> wrote:
>>  
>>> On Jul 18, 9:05 pm, oj <ojee... at gmail.com> wrote:
>>>
>>>
>>>
>>>    
>>>> On Jul 18, 11:33 am, arnimavidyar... at gmail.com wrote:
>>>>      
>>>>> Hi,
>>>>>         Hi,
>>>>>         I am taking a string as an input from the user and it 
>>>>> should only
>>>>> contain the chars:L , M or R
>>>>>         I tried the folllowing in kodos but they are still not 
>>>>> perfect:
>>>>>         [^A-K,^N-Q,^S-Z,^0-9]
>>>>> [L][M][R]
>>>>> [LRM]?L?[LRM]? etc but they do not exactly meet what I need.
>>>>>         For eg: LRLRLRLRLM is ok but LRLRLRNL is not as it has 'N' 
>>>>> .like that.
>>>>>         regards,
>>>>> SZ
>>>>>         The string may or may not have all the three chars.
>>>>>         
>>>> With regular expressions, [^LRM] matches a character that isn't L, R
>>>> or M. So:
>>>>       import re
>>>>       var = "LRLRLRLNR"
>>>>       if re.search(r'[^LRM]', var):
>>>>     print "Invalid"
>>>>       
>>> Fails if var refers to the empty string.
>>>     
>>
>> No it doesn't, it succeeds if var is an empty string. An empty string
>> doesn't contain characters that are not L, R or M.
>>
>> The OP doesn't specify whether an empty string is valid or not. My
>> interpretation was that an empty string would be valid.
>>   
> Why not just use * instead of + like:
>
> if re.search(r'^[^LRM]*$', var): # note: ^ outside [] is start of 
> string; $ means end of string
>    print "Invalid"
>
> This will *only* print invalid when there is a character other than L, 
> R, or M or a empty string.
>
Sorry, forget the beginning and ending markers, I just tried it out, it 
doesn't work.
use this instead:


if re.search(r'[^LRM]*', var):
   print "Invalid"