Hello,I was using configparser module in python3.6,but find it works not good when I try to write '%' to my config file,below is my func:

def update_config_file_key_value(file, section, key_name, key_value):
    # 通过configparser模块的调用更新配置文件
    # section是[]里面的值
    if os.path.exists(file) == False:
        os.system("touch %s" % file)
    import configparser
    config = configparser.ConfigParser()
    config.read(file)
    sectionList = config.sections()
    if section not in sectionList:
        config.add_section(section)
    config.set(section, key_name, str(key_value))
    with open(file, 'w') as f:
        config.write(f)

When I use it as:
update_config_file_key_value('config.ini','default','cookie',"123")
it works well,but below not ok:
update_config_file_key_value('config.ini','default','cookie',"%123")
and below not ok:
update_config_file_key_value('config.ini','default','cookie',"123%")
and below not ok:
update_config_file_key_value('config.ini','default','cookie',"12%3")

That's to say,configparser can not write '%' to config file.

With the default ConfigParser, we're using basic interpolation, as covered by:

https://docs.python.org/3/library/configparser.html#configparser.BasicInterpolation

To not have it, set interpolation to None in the ConfigParser constructor:

    config = configparser.ConfigParser(interpolation=None)

Then percent signs will be treated like any other character. Let me know if you have further questions.

Lukasz, this bug could be closed, couldn't it?