re question

[Schüle Daniel]

Hello,

consider the following code

>>re.search("[a-z](?i)[a-z]","AA")

<_sre.SRE_Mat ch object at 0x40177e20>

this gives a match
if we provide an extra group for the first character it still works

>>re.search(" ([a-z])(?i)[a-z]","AA").group(1 )

'A'

>>>

it doesn't matter where (?i) is placed, right?
the re engine would glance at once on the entire pattern string
analize it (complain if pattern doesn't make sense, eg invalid)
and it would be the same as if the option was given expicitely
as re.IGNORECASE.

Is there a way to switch-off the option resp.
switch-on the option in the middle of the pattern?

Regards, Daniel

[Jim Segrave]

Re: re question

In article <e8tn4k$1vo$1@n ews2.rz.uni-karlsruhe.de>,
Schüle Daniel <uval@rz.uni-karlsruhe.dewro te:

>Hello,
>
>consider the following code
>

>re.search("[a-z](?i)[a-z]","AA")

><_sre.SRE_Matc h object at 0x40177e20>
>
>this gives a match
>if we provide an extra group for the first character it still works
>

>re.search("([a-z])(?i)[a-z]","AA").group(1 )

>'A'

>>

>
>it doesn't matter where (?i) is placed, right?
>the re engine would glance at once on the entire pattern string
>analize it (complain if pattern doesn't make sense, eg invalid)
>and it would be the same as if the option was given expicitely
>as re.IGNORECASE.
>
>Is there a way to switch-off the option resp.
>switch-on the option in the middle of the pattern?

The docs say:

(?iLmsux)
(One or more letters from the set "i", "L", "m", "s", "u", "x".)
The group matches the empty string; the letters set the
corresponding flags (re.I, re.L, re.M, re.S, re.U, re.X) for the
^^^^^^^
entire regular expression. This is useful if you wish to include
^^^^^^^^^^^^^^^ ^^^^^^^^^^

the flags as part of the regular expression, instead of passing a
flag argument to the compile() function.


Some regex packages, but not Python's, support (?-<flag>) and this
allows turning the flag off and on for parts of the regex.



--
Jim Segrave (jes@jes-2.demon.nl)