def json_convertor (data, col_from, col_to):
    """
    This function is to use a two-columns pair to generate a json style string 
    that can be used in the .replace() function in pandas. 
    
    INPUT: 
        data: pandas DataFrame
        col_from: column name to be used as 'before-change-value'
        col_to: column name to be used as 'after-change-value'
    
    OUTPUT: 
        json_string_long: json style string
    """
    json_string_long = []
    data = data.reset_index()
    total_length = len(data)
    for i in range(total_length):
        """
        """
        json_string = "'" + data.loc[i, col_from] + "'" + ":" + \
                      "'" + data.loc[i, col_to] + "'"
        json_string_long.append(json_string)
    json_string_long = "{" + (',').join(json_string_long) + "}"
    
    return json_string_long