The problem is not the use of the raw string, but rather the regular expression inside it.
In regular expressions, the * means that whatever appears before it may be repeated zero or more times. So if you say H* that means zero or more H’s in a row. I think you mean an H followed by any number of other characters which would be H.* (the . matches any single character, so .* means zero or more of any characters). On the other hand, H\* means to match an H followed by a literal asterisk character. Does that help clarify why one matched and the other doesn’t? steve On 18-Feb-2014, at 10:09, Santosh Kumar <rhce....@gmail.com> wrote: > Steve, > > i am trying to under r - raw string notation. Am i understanding it wrong. > Rather than using "\", it says we can use the "r" option. > > http://docs.python.org/2/library/re.html > > Check the first paragraph for the above link. > > Thanks, > santosh > > > > On Tue, Feb 18, 2014 at 11:33 PM, Steve Willoughby <st...@alchemy.com> wrote: > Because the regular expression <H*> means “match an angle-bracket character, > zero or more H characters, followed by a close angle-bracket character” and > your string does not match that pattern. > > This is why it’s best to check that the match succeeded before going ahead to > call group() on the result (since in this case there is no result). > > > On 18-Feb-2014, at 09:52, Santosh Kumar <rhce....@gmail.com> wrote: > > > > > Hi All, > > > > If you notice the below example, case I is working as expected. > > > > Case I: > > In [41]: string = "<H*>test<H*>" > > > > In [42]: re.match('<H\*>',string).group() > > Out[42]: '<H*>' > > > > But why is the raw string 'r' not working as expected ? > > > > Case II: > > > > In [43]: re.match(r'<H*>',string).group() > > --------------------------------------------------------------------------- > > AttributeError Traceback (most recent call last) > > <ipython-input-43-d66b47f01f1c> in <module>() > > ----> 1 re.match(r'<H*>',string).group() > > > > AttributeError: 'NoneType' object has no attribute 'group' > > > > In [44]: re.match(r'<H*>',string) > > > > > > > > Thanks, > > santosh > > > > _______________________________________________ > > Tutor maillist - Tutor@python.org > > To unsubscribe or change subscription options: > > https://mail.python.org/mailman/listinfo/tutor > > > > > -- > D. Santosh Kumar > RHCE | SCSA > +91-9703206361 > > > Every task has a unpleasant side .. But you must focus on the end result you > are producing. >
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