def iso_reference_valid_char(c, raise_error=True):
if c in ISO_REFERENCE_VALID:<EOL><INDENT>return True<EOL><DEDENT>if raise_error:<EOL><INDENT>raise ValueError("<STR_LIT>" % (c, ISO_REFERENCE_VALID))<EOL><DEDENT>return False<EOL>
Helper to make sure the given character is valid for a reference number