Check for funny characters with a regexp

[joe_momma]

?
Causes the resulting RE to match 0 or 1 repetitions of the preceding RE. ab? will match either ‘a’ or ‘ab’.

from the docs python docs

>>> re.findall('(i?)[ā㥹ĆćČčĎďĐđēĕĖėęěĞğġīįİıĽľŁłŃńņňŋŌōőŒœŕřŚśŞşŠšŢţťŧũūŮűųŹźŻżŽžſ]', 'abcdefghijklmnopqrstuvwxyz')
[]

The solution chosen by the Perl developers was to use (?...) as the extension syntax. ? immediately after a parenthesis was a syntax error because the ? would have nothing to repeat, so this didn’t introduce any compatibility problems. The characters immediately after the ? indicate what extension is being used, so (?=foo) is one thing (a positive lookahead assertion) and (?:foo) is something else (a non-capturing group containing the subexpression foo).

from how to here