Called when if a binary operation is found.
        Only check for string formatting operations.

        @param node: currently checking node

def visit_binop(self, node):
        """
        Called when if a binary operation is found.
        Only check for string formatting operations.

        @param node: currently checking node
        """
        if node.op != "%":
            return
        pattern = node.left.as_string()
        # If the pattern's not a constant string, we don't know whether a
        # dictionary or a tuple makes sense, so don't try to guess.
        if not pattern.startswith("'") or pattern.startswith('"'):
            return
        # If the pattern has things like %(foo)s, then the values can't be a
        # tuple, so don't check for it.
        if "%(" in pattern:
            return
        valueString = node.right.as_string()
        tupleUsed = valueString.startswith('(')
        if tupleUsed:
            return
        self.add_message('W9501', node=node)