backreferences

[Amy Dillavou]

Can someone help me with understanding how python uses backreferences?
I need to remember the item that was last matched by the re engine but i
cant seem to understand anything that I find on backreferences. if I
want to access the last match do i use \number or is there something
else i have to do?

heres part of my code:
renDate = re.compile("$(( \d){4}-(\d){2}-(\d){2}))")
renDate.search( l)
if(exist.search (l) and str(lastmodDate ) < \1): #i need help here with \1

Thanks in advance
A.D

[Iain King]

Re: backreferences


Amy Dillavou wrote:[color=blue]
> Can someone help me with understanding how python uses backreferences?
> I need to remember the item that was last matched by the re engine but i
> cant seem to understand anything that I find on backreferences. if I
> want to access the last match do i use \number or is there something
> else i have to do?
>
> heres part of my code:
> renDate = re.compile("$(( \d){4}-(\d){2}-(\d){2}))")
> renDate.search( l)
> if(exist.search (l) and str(lastmodDate ) < \1): #i need help here with \1
>
> Thanks in advance
> A.D[/color]

I haven't had to use backreferences yet, so I don't know offhand how to
go about it. What I do know is that this online book is very useful:

http://gnosis.cx/TPiP/

Chapter 3 covers REs:

http://gnosis.cx/TPiP/chap3.txt

[color=blue]
>From what I remember, in python you can use numbered backreferences (up[/color]
to 99), or named ones.

Iain

[George Sakkis]

Re: backreferences


"Amy Dillavou" <gs2luv@line72. net> wrote in message
news:mailman.10 84.1127915597.5 09.python-list@python.org ...[color=blue]
> Can someone help me with understanding how python uses backreferences?
> I need to remember the item that was last matched by the re engine but i
> cant seem to understand anything that I find on backreferences. if I
> want to access the last match do i use \number or is there something
> else i have to do?
>
> heres part of my code:
> renDate = re.compile("$(( \d){4}-(\d){2}-(\d){2}))")
> renDate.search( l)
> if(exist.search (l) and str(lastmodDate ) < \1): #i need help here with \1
>
> Thanks in advance
> A.D[/color]

renDate = re.compile(some _regex)
match = renDate.search( input)
if match and str(lastmodDate ) < match.group(1):
do_something()


HTH,
George

[Amy Dillavou]

Re: backreferences

George and Iain -
Thanks for your help!!! It worked for me, and that book seems to be
really useful =)
A.D

On Wed, 2005-09-28 at 11:16 -0400, George Sakkis wrote:[color=blue]
> "Amy Dillavou" <gs2luv@line72. net> wrote in message
> news:mailman.10 84.1127915597.5 09.python-list@python.org ...[color=green]
> > Can someone help me with understanding how python uses backreferences?
> > I need to remember the item that was last matched by the re engine but i
> > cant seem to understand anything that I find on backreferences. if I
> > want to access the last match do i use \number or is there something
> > else i have to do?
> >
> > heres part of my code:
> > renDate = re.compile("$(( \d){4}-(\d){2}-(\d){2}))")
> > renDate.search( l)
> > if(exist.search (l) and str(lastmodDate ) < \1): #i need help here with \1
> >
> > Thanks in advance
> > A.D[/color]
>
> renDate = re.compile(some _regex)
> match = renDate.search( input)
> if match and str(lastmodDate ) < match.group(1):
> do_something()
>
>
> HTH,
> George
>
>[/color]

[Peter]

Re: backreferences

Iain King wrote:
[color=blue]
>Amy Dillavou wrote:
>
>[color=green]
>>Can someone help me with understanding how python uses backreferences?
>>I need to remember the item that was last matched by the re engine but i
>>cant seem to understand anything that I find on backreferences. if I
>>want to access the last match do i use \number or is there something
>>else i have to do?
>>
>>heres part of my code:
>>renDate = re.compile("$(( \d){4}-(\d){2}-(\d){2}))")
>>renDate.searc h(l)
>>if(exist.sear ch(l) and str(lastmodDate ) < \1): #i need help here with \1
>>
>>Thanks in advance
>>A.D
>>
>>[/color]
>
>I haven't had to use backreferences yet, so I don't know offhand how to
>go about it. What I do know is that this online book is very useful:
>
>http://gnosis.cx/TPiP/
>
>
>Chapter 3 covers REs:
>
>http://gnosis.cx/TPiP/chap3.txt
>[color=green]
>>From what I remember, in python you can use numbered backreferences (up[/color]
>to 99), or named ones.
>
>Iain
>
>
>[/color]
This shows both named backreferences and indexed. In both the
replacement and the searching.

(?P<name>data) sets the value of a named backreference named name to the
value of data (but can only be used in the pattern).

\NUMBER gets the value of a backreference by its index (can be used in
the pattern or the replacement).

(?P=name) gets the value of a named backreference (but only in the pattern).

\g<name> gets the value of a named backreference (but only in the
replacement).

Example:

re.sub(r"""<(?P <tag>H[1-5]) style="(.*)">(? P<text>.*)</(?P=tag)>""",
r"""<B style="\2">\g<t ext></B> | <\1 style="\2">\3<\ 1>""",
"""<H1 style="color: #000000">abc</H1>"""
)

HTH,
Peter