'Consume the text following a \'#\' as an error.
Looks for a match in self.ERROR_CODES and returns the number of
characters matched. (Does not update self.offset)'

def parse_error(self):

    self.assert_empty_token()
    assert (self.formula[self.offset] == '#')
    subformula = self.formula[self.offset:]
    for err in self.ERROR_CODES:
        if subformula.startswith(err):
            self.items.append(Token.make_operand(err))
            return len(err)
    raise TokenizerError(("Invalid    error    code    at    position    %d    in    '%s'" % (self.offset, self.formula)))
