Checks if value is a (quoted) string.

def isstring(args, quoted=False):
    """Checks if value is a (quoted) string."""
    isquoted = lambda c: c[0]==c[-1] and c[0] in ['"', "'"]

    if quoted:
        check = lambda c: isinstance(c, str) and isquoted(c)
    else:
        check = lambda c: isinstance(c, str)

    if isinstance(args, list):
        return all(map(check, args))
    else:
        return check(args)