Error in configparser

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I have a configuration file (abc.ini)as below

[DEFAULTS]
plus = plus.jpg

[PATHS]
folderPath = None

import configparser
config = configparser.ConfigParser()
config.read("abc.ini", encoding="utf-8")
print(config.sections())  # works ok
config["PATHS"].folder_path = path  # path is some path 

I don't understand whats happening in config["PATHS"].folder_path = path
when I do config["PATHS"]["folder_path"] I am getting an error.

Also, to access a value, we can use config["PATHS"]["folderPath"]
but can't we use config["PATHS"].folderPath