Checks the flow operator ('>') to make sure that it:
    1) Is non empty
    2) There is only one of them

def _check_flow_operator(string):
    """
    Checks the flow operator ('>') to make sure that it:
    1) Is non empty
    2) There is only one of them
    """
    greater_than_count = string.count('>')
    if greater_than_count > 1:
        raise ValueError(MULTIPLE_FLOW_OPERATORS)
    elif (string[0] == '>') or (string[-1] == '>'):
        raise ValueError(FLOW_OPERATOR_ON_ENDS)
    else:
        if greater_than_count == 1:
            ret = True
        else:
            ret = False
    return ret