Re: trying to match a string
On Jul 19, 3:04 am, Andrew Freeman [EMAIL PROTECTED] wrote: let me revise it please: To show if valid: if re.search(r'^[LRM]*$', 'LM'): print 'Valid' Fine, this works, although match instead of search blah blah blah as has already been mentioned. I still think searching for one invalid character is more elegant then trying to match the entire string, but that's just personal preference, I guess. To show if invalid, if re.search(r'^[^LRM]*$', '0'): print 'Inalid' No. This is wrong. This only matches strings that consist entirely of characters that are not L, R or M: import re if re.search(r'^[^LRM]*$', 'ZZZLZZZ'): ... print Invalid ... This doesn't print Invalid because there is one non-invalid character there, which is clearly not what the OP wanted. -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
oj wrote: Fine, this works, although match instead of search blah blah blah as has already been mentioned. I still think searching for one invalid character is more elegant then trying to match the entire string, but that's just personal preference, I guess. The drawback is that it's a lot easier to mess up the edge cases if you do that (as this thread has shown). The small speedup you get in typical cases is quickly offset by extra debugging/testing time (or, for that matter, arguing with c.l.py:ers over more or less contrived ways to interpret the original post). Guess it's up to personal preferences for how to best help others. Unless the OP explicitly asks for something else, I prefer to use simple and straight-forward solutions with reasonable execution behaviour over clever tricks or odd-ball solutions; it's not a JAPH contest, after all. /F -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
On Jul 21, 11:04 am, Fredrik Lundh [EMAIL PROTECTED] wrote: The drawback is that it's a lot easier to mess up the edge cases if you do that (as this thread has shown). The small speedup you get in typical cases is quickly offset by extra debugging/testing time (or, for that matter, arguing with c.l.py:ers over more or less contrived ways to interpret the original post). I disagree, from this thread, most of the erroneous solutions have been attempts to match the entire string. Guess it's up to personal preferences for how to best help others. Unless the OP explicitly asks for something else, I prefer to use simple and straight-forward solutions with reasonable execution behaviour over clever tricks or odd-ball solutions; it's not a JAPH contest, after all. [^LRM] *is* a simple and straight-forward regex - it isn't attempting to do any clever tricks or anything odd-ball. That said, I still think the sets solution is more elegant then the regex solutions. -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
John Machin wrote: On Jul 20, 11:14 am, Andrew Freeman [EMAIL PROTECTED] wrote: John Machin wrote: (4) I highly doubt that this code was actually to be used in an interactive session, The offending code is a nonsense wherever it is used. the False/True output was truncated intentionally, What meaning are you attaching to truncated? I'm attaching the meaning of deleted the line (manually (not in python)) to truncated, I'm actually using ipython, but though it would be a good practice to type it out as if it come from the standard interpretor. I also though it would be OK to leave out some output which I considered unnecessary. -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
John Machin wrote: On Jul 19, 12:04 pm, Andrew Freeman [EMAIL PROTECTED] wrote: To show if valid: if re.search(r'^[LRM]*$', 'LM'): print 'Valid' A couple of points: (1) Instead of search(r'^blahblah', ...) use match(r'blahblah', ...) (2) You need to choose your end-anchor correctly; your pattern is permitting a newline at the end: re.search(r'^[LRM]*$', 'LM\n') _sre.SRE_Match object at 0x00B9E528 -- http://mail.python.org/mailman/listinfo/python-list Thanks for your pointers, however have a question regarding the first: import re def my_match(var):# my original if re.search(r'^[LRM]*$', 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(eg) Valid # correct! other_match(fg) 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(fg) Invalid final_match(eg + '\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 -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
Andrew Freeman wrote: John Machin wrote: A couple of points: (1) Instead of search(r'^blahblah', ...) use match(r'blahblah', ...) (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 -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
On Jul 20, 5:00 am, Andrew Freeman [EMAIL PROTECTED] wrote: Andrew Freeman wrote: John Machin wrote: A couple of points: (1) Instead of search(r'^blahblah', ...) use match(r'blahblah', ...) (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(zeroplusLRM, alist) ['LLMMRR', 'L'] [x for x in alist if zeroplusLRM(x)] ['LLMMRR', 'L'] Cheers, John -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
John Machin wrote: On Jul 20, 5:00 am, Andrew Freeman [EMAIL PROTECTED] wrote: Andrew Freeman wrote: John Machin wrote: A couple of points: (1) Instead of search(r'^blahblah', ...) use match(r'blahblah', ...) (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(zeroplusLRM, alist) ['LLMMRR', 'L'] [x for x in alist if zeroplusLRM(x)] ['LLMMRR', 'L'] Thank you for the pointers! (1) Depending on the typeface I totally agree, Courier New has a nearly indistinguishable 1 and l, I'm using Dejavu Sans Mono (Bitstream Vera based). I was just thinking of it as a generic variable name for some input. I'm fairly new to python and programming in general, it's more of a hobby. (2-3) This is actually the first time I've used map, maybe I should not give extra examples, I was actually using it as a learning tool for myself. I'm very thankful the mailing list has such skilled contributers, such as yourself, but I assume that it can't hurt to give working code, even though the style is less than perfect. (3) Personally I think map(lambda i: match(i)==False or out.append(i), l) is a little more readable than map(lambda i: not match(i) or out.append(i), l) even if baroque, your use of filter is obviously much clearer than either. (4) I highly doubt that this code was actually to be used in an interactive session, the False/True output was truncated intentionally, it's an obvious, but superfluous output (unless you were to rely on this by attaching it to a variable which might lead to sorting issues). (5) Thank you very much, I've read of the filter and reduce functions, but haven't used them enough to recognize their usefulness. I did realize that a list comprehension would be useful, but wanted to try map() I put together a generic matcher that returns either a list of True data (if the input is a list or tuple) or a boolean value: def match(ex, var): ex is the regular expression to match for, var the iterable or string to return a list of matching items or a boolean value respectively. ex = re.compile(ex).match if isinstance(var, (list, tuple)): return filter(ex, var) else: return bool(ex(var)) I believe this is fairly clean and succinct code, it would help my learning immensely if you feel there is a more succinct, generic way of writing this function. -- Andrew -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
On Jul 20, 11:14 am, Andrew Freeman [EMAIL PROTECTED] wrote: John Machin wrote: (4) I highly doubt that this code was actually to be used in an interactive session, The offending code is a nonsense wherever it is used. the False/True output was truncated intentionally, What meaning are you attaching to truncated? it's an obvious, but superfluous output (unless you were to rely on this by attaching it to a variable which might lead to sorting issues). I put together a generic matcher that returns either a list of True data (if the input is a list or tuple) or a boolean value: def match(ex, var): ex is the regular expression to match for, var the iterable or string to return a list of matching items or a boolean value respectively. ex = re.compile(ex).match You lose clarity by rebinding ex like that, and you gain nothing. if isinstance(var, (list, tuple)): return filter(ex, var) else: return bool(ex(var)) I believe this is fairly clean and succinct code, it would help my learning immensely if you feel there is a more succinct, generic way of writing this function. You have created a function which does two quite different things depending on whether one of the arguments is one of only two of the many kinds of iterables and which has a rather generic (match what?) and misleading (something which filters matches is called match??) name. The loss of clarity and ease of understanding caused by the readers having to find the code for the function so that they can puzzle through it means that the most succinct, generic and *recommended* way of writing this function would be not to write it at all. Write a function which returns a MatchObject. In the unlikely event that that anyone really wants to put bools in a list and sort them, then they can wrap bool() around it. Give it a meaningful name e.g. match_LRM. You want to check if a single variable refers to a valid LRM string? Use match_LRM(the_variable). Nice and clear. You want to filter out of some iterable all the occurrences of valid LRM strings? Use filter (whose name indicates its task) or a generator or list comprehension ... what [x for x in some_iterable if match_LRM(x)] does should be screamingly obvious i.e. have less chance than filter of needing a trip to the manual. HTH, John -- http://mail.python.org/mailman/listinfo/python-list
trying to match a string
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. -- http://mail.python.org/mailman/listinfo/python-list
trying to match a string
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. -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
[EMAIL PROTECTED] writes:
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.
var = 'LRLRLRNL'
residue = var.replace('L','').replace('R','').replace('M','')
if residue != '':
... print 'Invalid characters in input',residue
...
Invalid characters in input N
--
http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
On Jul 18, 8:33 pm, [EMAIL PROTECTED] 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. -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
On Jul 18, 11:33 am, [EMAIL PROTECTED] 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 -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
On Jul 18, 3:46 pm, [EMAIL PROTECTED] (Eddie Corns) wrote:
[EMAIL PROTECTED] writes:
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.
var = 'LRLRLRNL'
residue = var.replace('L','').replace('R','').replace('M','')
if residue != '':
... print 'Invalid characters in input',residue
...
Invalid characters in input N
That was quick.Thanks.Never thought it that angle :(
--
http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
On Jul 18, 9:05 pm, oj [EMAIL PROTECTED] wrote: On Jul 18, 11:33 am, [EMAIL PROTECTED] 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. -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
On Jul 18, 12:10 pm, John Machin [EMAIL PROTECTED] wrote: On Jul 18, 9:05 pm, oj [EMAIL PROTECTED] wrote: On Jul 18, 11:33 am, [EMAIL PROTECTED] 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. -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
[EMAIL PROTECTED] wrote:
I am taking a string as an input from the user and it should only
contain the chars:L , M or R
How about skipping re's and doing something like:
set(input_string) = set('LMR')
If you want to disallow the empty string:
set([]) set(input_string) = set('LMR')
--Scott David Daniels
[EMAIL PROTECTED]
--
http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
oj wrote: On Jul 18, 12:10 pm, John Machin [EMAIL PROTECTED] wrote: On Jul 18, 9:05 pm, oj [EMAIL PROTECTED] wrote: On Jul 18, 11:33 am, [EMAIL PROTECTED] 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. -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
Andrew Freeman wrote: oj wrote: On Jul 18, 12:10 pm, John Machin [EMAIL PROTECTED] wrote: On Jul 18, 9:05 pm, oj [EMAIL PROTECTED] wrote: On Jul 18, 11:33 am, [EMAIL PROTECTED] 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 -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
On Jul 18, 7:51 pm, Andrew Freeman [EMAIL PROTECTED] wrote: Andrew Freeman wrote: oj wrote: On Jul 18, 12:10 pm, John Machin [EMAIL PROTECTED] wrote: On Jul 18, 9:05 pm, oj [EMAIL PROTECTED] wrote: On Jul 18, 11:33 am, [EMAIL PROTECTED] 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. -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
On Jul 18, 7:51 am, Andrew Freeman [EMAIL PROTECTED] wrote: Andrew Freeman wrote: oj wrote: On Jul 18, 12:10 pm, John Machin [EMAIL PROTECTED] wrote: On Jul 18, 9:05 pm, oj [EMAIL PROTECTED] wrote: On Jul 18, 11:33 am, [EMAIL PROTECTED] 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. -- http://mail.python.org/mailman/listinfo/python-list
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. -- http://mail.python.org/mailman/listinfo/python-list
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]*$', var): ... print 'Valid' ... else: ... print 'Invalid' eg = 'LRLRLRLRLM' match(eg) Valid fg = 'LRLRLRNL' match(fg) Invalid -- Andrew -- http://mail.python.org/mailman/listinfo/python-list
Re: trying to match a string
On Jul 19, 12:04 pm, Andrew Freeman [EMAIL PROTECTED] wrote: To show if valid: if re.search(r'^[LRM]*$', 'LM'): print 'Valid' A couple of points: (1) Instead of search(r'^blahblah', ...) use match(r'blahblah', ...) (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_Match object at 0x00B9E528 -- http://mail.python.org/mailman/listinfo/python-list
