Finding strings with exceptions

[Henrik Motakef]

David Brady <daves_spam_dodging_account at yahoo.com> writes:

> The old class name (changed to protect the innocent)
> is BarThingy.  The new name is fooBarThingy.  Because
> the new class name contains the old one, simple
> find-and-replace goes wonky.  In the reverse case, I
> could put something in the regex that says, "also find
> an optional prefix 'foo'."  But what I really want to
> do is find the class everywhere EXCEPT where that
> 'foo' prefix exists.  Anyone know a good way to do
> this?

What you are looking for is called a "negative lookbehind
assertion, and looks like this:

>>> import re
>>> re.compile("(?<!foo)BarThingy")
>>> re.search("fooBarThingie")
>>> re.search("BarThingie")
<SRE_Match object at 0x501c0>

Nice syntax, huh?

hth
Henrik