Raw string substitution problem

[Alan G Isaac]

On 12/17/2009 2:45 PM, MRAB wrote:
> re.compile('a\\nc') _does_ compile to the same as regex as
> re.compile('a\nc').
>
> However, regex objects never compare equal to each other, so, strictly
> speaking, re.compile('a\nc') != re.compile('a\nc').
>
> However, having said that, the re module contains a cache (keyed on the
> string and options supplied), so the first re.compile('a\nc') will put
> the regex object in the cache and the second re.compile('a\nc') will
> return that same regex object from the cache. If you clear the cache in
> between the two calls (do re._cache.clear()) you'll get two different
> regex objects which won't compare equal even though they are to all
> intents identical.


OK, this is helpful.
(I did check equality but did not understand
I got True only because re used caching.)
So is the bottom line the following?
A string replacement is not just "converted"
as described in the documentation, essentially
it is compiled?

But that cannot quite be right.  E.g., \b will be a back
space not a word boundary.  So then the question arises
again, why isn't '\\' a backslash? Just because?
Why does it not get the "obvious" conversion?

Thanks,
Alan Isaac