[Tutor] Why doesn't this regex match???

[Kirby Urner]

>
>So I tried the following, with the dismal results shown. Now what am I
>doing wrong?
>
> >>> searchstring = 'ADV: FREE FREE OFFERZ!!!!'
> >>> word = 'adv:'
> >>> p = re.compile(r'[\b\A\s]%s[\b\Z\s]' % word, re.I)
>Traceback (most recent call last):
>   File "<pyshell#45>", line 1, in ?
>     p = re.compile(r'[\b\A\s]%s[\b\Z\s]' % word, re.I)
>   File "E:\PYTHON\PYTHON22\lib\sre.py", line 178, in compile
>     return _compile(pattern, flags)
>   File "E:\PYTHON\PYTHON22\lib\sre.py", line 228, in _compile
>     raise error, v # invalid expression
>error: internal: unsupported set operator

At this point, I share your confusion.  Using your same values:

 >>> p = re.compile(r'\A%s' % word, re.I)      # works
 >>> p = re.compile(r'[\A]%s' % word, re.I)    # finds nothing
 >>> p = re.compile(r'[\A]*%s' % word, re.I)   # works
 >>> p = re.compile(r'[\A]?%s' % word, re.I)   # works

? and * both match 0 times, as well as 1 or many respectively.
But if \A is not there at all, why does the first pattern work?
If \A is there, why does the 2nd pattern fail?

Something about p = re.compile(r'[\s\A]') is invalid.

I'm not sure what.

Kirby