Negative regular expressions (searching for "i" not inside command)

[Bart Kastermans]

I have a file in which I am searching for the letter "i" (actually
a bit more general than that, arbitrary regular expressions could
occur) as long as it does not occur inside an expression that matches
\\.+?\b (something started by a backslash and including the word that
follows).

More concrete example, I have the string "\sin(i)" and I want to match
the argument, but not the i in \sin.

Can this be achieved by combining the regular expressions? I do not
know the right terminology involved, therefore my searching on the
Internet has not led to any results.

I can achieve something like this by searching for all i and then
throwing away those i that are inside such expressions. I am now just
wondering if these two steps can be combined into one.

Best,
Bart
--
http://www.bartk.nl/

[Guilherme Polo]

On Thu, Aug 28, 2008 at 5:04 PM, Bart Kastermans
<ka******@math.wisc.edu${hostname}wrote:

I have a file in which I am searching for the letter "i" (actually
a bit more general than that, arbitrary regular expressions could
occur) as long as it does not occur inside an expression that matches
\\.+?\b (something started by a backslash and including the word that
follows).

More concrete example, I have the string "\sin(i)" and I want to match
the argument, but not the i in \sin.

Can this be achieved by combining the regular expressions? I do not
know the right terminology involved, therefore my searching on the
Internet has not led to any results.

Try searching again with the "lookahead" term, or "negative lookahead".

>
I can achieve something like this by searching for all i and then
throwing away those i that are inside such expressions. I am now just
wondering if these two steps can be combined into one.

Best,
Bart
--
http://www.bartk.nl/
--
http://mail.python.org/mailman/listinfo/python-list

--
-- Guilherme H. Polo Goncalves

[castironpi]

On Aug 28, 4:04*pm, "Guilherme Polo" <[e-mail]:

On Thu, Aug 28, 2008 at 5:04 PM, Bart Kastermans

<[e-mail]${hostname}wrote:

I have a file in which I am searching for the letter "i" (actually
a bit more general than that, arbitrary regular expressions could
occur) as long as it does not occur inside an expression that matches
\\.+?\b (something started by a backslash and including the word that
follows).

More concrete example, I have the string "\sin(i)" and I want to match
the argument, but not the i in \sin.

Can this be achieved by combining the regular expressions? *I do not
know the right terminology involved, therefore my searching on the
Internet has not led to any results.

Try searching again with the "lookahead" term, or "negative lookahead".

I can achieve something like this by searching for all i and then
throwing away those i that are inside such expressions. *I am now just
wondering if these two steps can be combined into one.

Best,
Bart
--
http://www.bartk.nl/
--
http://mail.python.org/mailman/listinfo/python-list

--
-- Guilherme H. Polo Goncalves

No dice: "This is called a positive lookbehind assertion. ...The
contained pattern must only match strings of some fixed length."
'finditer' could make the 'combined into one' option more attractive
though.