Simple regular expression

John Machin sjmachin at lexicon.net
Fri Jun 27 22:00:49 CEST 2008


On Jun 28, 2:26 am, python_enthu <srhe... at gmail.com> wrote:
> On Jun 27, 11:05 am, "John Salerno" <johnj... at NOSPAMgmail.com> wrote:
>
>
>
> > "python_enthu" <srhe... at gmail.com> wrote in message
>
> >news:47031cc4-2b5e-43b3-9338-cf4a7b4c1568 at d45g2000hsc.googlegroups.com...
>
> > >I am trying this.. what is wrong in this..
>
> > > IDLE 1.2.2
> > >>>> import re
> > >>>> a="my name is fname lname"
> > >>>> p=re.compile('name')
> > >>>> m=p.match (a)
> > >>>> print p.match(a)
> > > None
>
> >       match( string[, pos[, endpos]])
>
> > If zero or more characters at the beginning of string match this regular
> > expression, return a corresponding MatchObject instance. Return None if the
> > string does not match the pattern; note that this is different from a
> > zero-length match.
>
> >       search( string[, pos[, endpos]])
>
> > Scan through string looking for a location where this regular expression
> > produces a match, and return a corresponding MatchObject instance. Return
> > None if no position in the string matches the pattern; note that this is
> > different from finding a zero-length match at some point in the string.
>
> Thanks John Salerno and John Machin,
>
> I am used to perl. So I guess I am better of using re.search instead
> of re.match
> BTW, is re.search('string') equivalent to re.match ('^string')

No. Perhaps you meant "is re.search('^string') equivalent to
re.match('string')"?

There are functional differences, which are documented in the section
of the manual to which I referred you.

There is currently (2.5.2) a speed penalty for not reading the manual:

C:\junk>python -m timeit -s "import
re;rx=re.compile(r'y');t='x'*100000" "rx.match(t)"
1000000 loops, best of 3: 1.08 usec per loop

C:\junk>python -m timeit -s "import
re;rx=re.compile(r'y');t='x'*10000000" "rx.match(t)"
1000000 loops, best of 3: 1.07 usec per loop

C:\junk>python -m timeit -s "import
re;rx=re.compile(r'^y');t='x'*100000" "rx.search(t)"
100 loops, best of 3: 2.76 msec per loop

C:\junk>python -m timeit -s "import
re;rx=re.compile(r'^y');t='x'*10000000" "rx.search(t)"
10 loops, best of 3: 277 msec per loop

... and no queue of petitioners requesting an enhancement.

Cheers,
John



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