trying to match a string

[arnimavidyarthy@gmail.com]

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.

[John Machin]

Re: trying to match a string

On Jul 18, 8:33 pm, arnimavidyar... @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.

re.match(r'[LMR]+\Z', your_string)

in English: one or more of L, M , or R, followed by the end of the
string.

[oj]

Re: trying to match a string

On Jul 18, 11:33 am, arnimavidyar... @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"

[John Machin]

Re: trying to match a string

On Jul 18, 9:05 pm, oj <ojee...@gmail. comwrote:

On Jul 18, 11:33 am, arnimavidyar... @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.

[oj]

Re: trying to match a string

On Jul 18, 12:10 pm, John Machin <sjmac...@lexic on.netwrote:

On Jul 18, 9:05 pm, oj <ojee...@gmail. comwrote:
>
>
>

On Jul 18, 11:33 am, arnimavidyar... @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.

[Andrew Freeman]

Re: trying to match a string

oj wrote:

On Jul 18, 12:10 pm, John Machin <sjmac...@lexic on.netwrote:
>

>On Jul 18, 9:05 pm, oj <ojee...@gmail. comwrote:
>>
>>
>>
>>

>>On Jul 18, 11:33 am, arnimavidyar... @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.

[Andrew Freeman]

Re: trying to match a string

Andrew Freeman wrote:

oj wrote:

>On Jul 18, 12:10 pm, John Machin <sjmac...@lexic on.netwrote:
>>

>>On Jul 18, 9:05 pm, oj <ojee...@gmail. comwrote:
>>>
>>>
>>>
>>>
>>>On Jul 18, 11:33 am, arnimavidyar... @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
>interpretati on 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"

[arni]

Re: trying to match a string

On Jul 18, 7:51 pm, Andrew Freeman <alif...@gmail. comwrote:

Andrew Freeman wrote:

oj wrote:

On Jul 18, 12:10 pm, John Machin <sjmac...@lexic on.netwrote:

>

>On Jul 18, 9:05 pm, oj <ojee...@gmail. comwrote:

>

>>On Jul 18, 11:33 am, arnimavidyar... @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"

I was using kodos to check the regex.I should have used the IDE
instead.Thanks a lot again.

[John S]

Re: trying to match a string

On Jul 18, 7:51 am, Andrew Freeman <alif...@gmail. comwrote:

Andrew Freeman wrote:

oj wrote:

On Jul 18, 12:10 pm, John Machin <sjmac...@lexic on.netwrote:

>

>On Jul 18, 9:05 pm, oj <ojee...@gmail. comwrote:

>

>>On Jul 18, 11:33 am, arnimavidyar... @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"

This won't work -- every string in the universe contains 0 or more
characters which are not 'L', 'R', or 'M'. That is, the regular
expression X* could match the empty string, which can be found in all
strings.

[oj]

Re: trying to match a string

>

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"

No, that's broken.

That searches for any number of invalid characters. Even 0, so it
ALWAYS matches, no matter what string you give it.

My regex worked in the first place, you're complicating it needlessly.
The presence of one invalid character makes the string invalid, so why
not just search for one? Similarly, there's no need to stick in the
beginning and end markers - you're not trying to match the entire
string, just find part of it that is invalid.

However, I think the sets solution by Scott David Daniels is the most
elegant method put forward.

[Andrew Freeman]

Re: trying to match a string

oj wrote:

>>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"
>>

>
No, that's broken.
>
That searches for any number of invalid characters. Even 0, so it
ALWAYS matches, no matter what string you give it.
>
My regex worked in the first place, you're complicating it needlessly.
The presence of one invalid character makes the string invalid, so why
not just search for one? Similarly, there's no need to stick in the
beginning and end markers - you're not trying to match the entire
string, just find part of it that is invalid.
>
However, I think the sets solution by Scott David Daniels is the most
elegant method put forward.
--

http://mail.python.org/mailman/listinfo/python-list

>

I see your point after rereading the question, he only wants to match L
R and M
let me revise it please:

To show if valid:

if re.search(r'^[LRM]*$', 'LM'):
print 'Valid'

To show if invalid,

if re.search(r'^[^LRM]*$', '0'):
print 'Inalid'

Example session:

>>import re
>>def match(var):
>> if re.search(r'^[LRM]*$', var):

........ print 'Valid'
........ else:
........ print 'Invalid'

>>>
>>eg = 'LRLRLRLRLM'
>>match(eg)

Valid

>>fg = 'LRLRLRNL'
>>match(fg)

Invalid
--
Andrew

[John Machin]

Re: trying to match a string

On Jul 19, 12:04 pm, Andrew Freeman <alif...@gmail. comwrote:

To show if valid:
>
if re.search(r'^[LRM]*$', 'LM'):
print 'Valid'
>

A couple of points:
(1) Instead of search(r'^blahb lah', ...) use match(r'blahbla h', ...)
(2) You need to choose your end-anchor correctly; your pattern is
permitting a newline at the end:

>>re.search(r '^[LRM]*$', 'LM\n')

<_sre.SRE_Mat ch object at 0x00B9E528>

>>>

[Andrew Freeman]

Re: trying to match a string

John Machin wrote:

On Jul 19, 12:04 pm, Andrew Freeman <alif...@gmail. comwrote:
>

>To show if valid:
>>
>if re.search(r'^[LRM]*$', 'LM'):
> print 'Valid'
>>
>>

>
A couple of points:
(1) Instead of search(r'^blahb lah', ...) use match(r'blahbla h', ...)
(2) You need to choose your end-anchor correctly; your pattern is
permitting a newline at the end:
>
>

>>>re.search(r' ^[LRM]*$', 'LM\n')
>>>>

<_sre.SRE_Mat ch object at 0x00B9E528>
>
--

http://mail.python.org/mailman/listinfo/python-list

>

Thanks for your pointers, however have a question regarding the first:

>>import re
>>def my_match(var): # my original
>> if re.search(r'^[LRM]*$', var):
>> print 'Valid'
>> else:
>> print 'invalid'
>>def other_match(var ): # your suggestion, I believe
>> if re.search(r'[LRM]*$', var):
>> print 'Valid'
>> else:
>> print 'Invalid'
>>>
>>eg = 'LRLRLRLRLM'
>>fg = 'LRLRLRNL'
>>my_match(eg )

Valid # correct!

>>my_match(fg )

Invaild # correct!

>>>
>>other_match(e g)

Valid # correct!

>>other_match(f g)

Vaild # INCORRECT, please explain

I believe other_match was your suggestion; to remove the ^
my_match is just a renamed version of my original function

Point 2:
Yes, I totally agree with you on point 2, let me try to combine my
knowledge and make a satisfactory function.

>>def final_match(var ):
>> if re.search(r'^[LRM]*\Z', var): # replace $ with \Z to limit

newlines
.... print 'Valid'
.... else:
.... print 'Invalid'

>> final_match(eg)

Valid

>>final_match(f g)

Invalid

>>final_match(e g + '\n')

Invalid

So, in conclusion, is this function satisfactory?

def match(var):
if re.search(r'^[LRM]*\Z', var):
print 'Valid'
else:
print 'Invalid'
--
Andrew

[Andrew Freeman]

Re: trying to match a string

Andrew Freeman wrote:

John Machin wrote:

>A couple of points:
>(1) Instead of search(r'^blahb lah', ...) use match(r'blahbla h', ...)
>(2) You need to choose your end-anchor correctly; your pattern is
>permitting a newline at the end:

I forgot to change search to match. This should be better:

def match(var):
if re.match(r'[LRM]*\Z', var):
return True
else:
return False

I was also thinking if you had a list of these items needing to be
verified you could use this:

>>l = ['LLMMRR', '00thLL', 'L', '\n']
>>out = []
>>map(lambda i: match(i)==False or out.append(i), l)
>>print out

['LLMMRR', 'L']

--
Andrew

[John Machin]

Re: trying to match a string

On Jul 20, 5:00 am, Andrew Freeman <alif...@gmail. comwrote:

Andrew Freeman wrote:

John Machin wrote:

A couple of points:
(1) Instead of search(r'^blahb lah', ...) use match(r'blahbla h', ...)
(2) You need to choose your end-anchor correctly; your pattern is
permitting a newline at the end:

>
I forgot to change search to match. This should be better:
>
def match(var):
if re.match(r'[LRM]*\Z', var):
return True
else:
return False

A bit wordy ...

if blahblah:
return True
else:
return False

can in total generality be replaced by:

return blahblah

>
I was also thinking if you had a list of these items needing to be
verified you could use this:

You could, but I suggest you don't use it in a job interview :-)

>>l = ['LLMMRR', '00thLL', 'L', '\n']

(1) Don't use 'L'.lower() as a name; it slows down reading as people
need to fire up their mental parser to distinguish it from the result
of 3 - 2

>>out = []
>>map(lambda i: match(i)==False or out.append(i), l)

(2) Read PEP 8
(3) blahblah == False ==not blahblah
(4) You didn't show the output from map() i.e. something like [None,
True, None, True]
(5) or out.append(...) is a baroque use of a side-effect, and is quite
unnecessary. If you feel inexorably drawn to following the map way,
read up on the filter and reduce functions. Otherwise learn about list
comprehensions and generators.

>>print out

['LLMMRR', 'L']
>

Consider this:

>>import re
>>alist = ['LLMMRR', '00thLL', 'L', '\n']
>>zeroplusLRM = re.compile(r'[LRM]*\Z').match
>>filter(zeropl usLRM, alist)

['LLMMRR', 'L']

>>[x for x in alist if zeroplusLRM(x)]

['LLMMRR', 'L']

>>>

Cheers,
John