Question

I need a regular expression to test if strings are in a specific palette of values for example string dir ca only be ltr, rtl, lro, rlo, or another example bool can be only false, true.

What regular expression, can I use to test a string like dir and bool against a limited set of values?

Answer 1

Do you mean something like '^(ltr|rtl|lro|rlo)$' and '^(true|false)$'?

this can even be easily automated:

def make_re(args):
    args = (re.escape(arg) for arg in args) #if you want to escape special characters
    return re.compile('^({0})$'.format('|'.join(args)) )

boolre = make_re(('true','false'))

However, if you leave the line args = (re.escape(arg) ...) in there, then you really don’t gain anything beyond what you could get using if arg in myset: .... The beauty of the unescaped version is that you still have at least some of the regex flexibility.