"\W" regex pattern, when used with `re.ASCII`, is expected to have the same behavior as "[^a-zA-Z0-9_]" (see [1]).

For example, the following `sub()` call

```
>>> re.sub('\W', '', '½ a', re.ASCII)
'½a'
```

should return the same as this one:

```
>>> re.sub('[^a-zA-Z0-9_]', '', '½ a', re.ASCII)
'a'
```

But it does not.

[1] https://docs.python.org/3/library/re.html#regular-expression-syntax

It works as expected:

>>> re.sub(r'\W', '', '½ a', 0, re.ASCII)
'a'

You just passed re.ASCII as the count argument, not as the flags argument.

>>> help(re.sub)
Help on function sub in module re:

sub(pattern, repl, string, count=0, flags=0)
    Return the string obtained by replacing the leftmost
    non-overlapping occurrences of the pattern in string by the
    replacement repl.  repl can be either a string or a callable;
    if a string, backslash escapes in it are processed.  If it is
    a callable, it's passed the Match object and must return
    a replacement string to be used.