Using ConfigParser With .ini Files

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The Newbie Method

A lot of the time when you are making something in Python, there is information that you want the user to be able to modify or keep separate from the program itself. Probably the simplest (and insecure) way to do this would be to just create a file called “config.py” and put all your values in there:

credentials = {"username":"AeroBlue", "email": "example@aeroblue.dev", "password": "password123"}
settings = {"login_prompt": "No"}

from config import settings, credentials
def main():
    print(credentials)
    print(settings)
main()
{"username":"AeroBlue", "email": "example@aeroblue.dev", "password": "password123"}
{"login_prompt": "No"}

Although this method works, DO NOT DO THIS. There is a built-in library in Python that will do all of this for you and provides many more features. The library is called ConfigParser.

ConfigParser (An Introduction)

There are a lot of ways you can set up your configuration file, but I like using .ini’s because they are simple and easy to understand. Let’s try this example again, but this time let’s use ConfigParser instead:

[credentials]
username = AeroBlue
email = example@aeroblue.dev
password = password123

[settings]
login_prompt = No

Note: Never store passwords and important data in config.ini you should be using environment variables. Only store config related values in plain text.

from configparser import ConfigParser

config = ConfigParser()
config.read_file(open("config.ini"))

Retrieving Values

Each time the program is run, we will first need to create an instance of ConfigParser() and use the read_file() method to parse our .ini file. Once we executed the two lines above, we can then access the values in a “dictionary-like” fashion:

username = config["credentials"]["username"]
email = config["credentials"]["email"]
password = config["credentials"]["password"]

However, we could do this a lot more efficiently by simultaneously unpacking all of the values in the credential section:

username, email, password = config["credentials"].values()

Both methods have the same result:

>>> print(f"Username: {username}")
Username: AeroBlue
>>> print(f"Email: {email}")
Email: example@aeroblue.dev
>>> print(f"Password: {password}")
Password: password123

Updating Values

Just like an actual dictionary, you can update values as well. For example, let’s say the user decides to set login_prompt to yes. We can update the credentials using the builtin input() method:

if config["settings"]["login_prompt"].lower() == "yes":
    config["credentials"]["username"] = str(input("Username: "))  # AeroBlue
    config["credentials"]["password"] = str(input("Password: "))  # password123
    config["settings"]["login_prompt"] = "no"  # Set to not prompt in the future

Saving the Config

With the code above, we are able to gather input from the user in the form of a string (the user’s username and password in the example) and then update the dictionary values. If you run the above code, nothing in the config file will be changed, we only need to add a couple more lines to update the current file:

with open('config.ini', 'w') as configfile:
    config.write(configfile)

Now if we open up the config file again, we can see that our changes have been updated! We have also updated the login_prompt option to no so that the user is not prompted until they set it again.

[credentials]
username = AeroBlue
email = example@aeroblue.dev
password = password123

[settings]
login_prompt = no

Interpolation

Not convinced on ConfigParser yet? I have one word for you, interpolation. ConfigParser even allows you to set and use values within the ini file itself! For this example I am going to slightly modify the ini file to demonstrate using interpolation in ConfigParser:

[credentials]
website = aeroblue.dev
username = Aero
email = %(username)s@%(website)s
password = password123

The important piece of code here is email = %(username)s@%(website)s, this is an example of using variables within the config file itself. This way a user can update something like their username, and it will automatically use it as their email too:

>>> print(f"Email: {email}")
Aero@aeroblue.dev

Conclusion

While there are a few other things you can do with ConfigParser, this is meant to be an introductory guide to help you write your first config file. Hopefully, this was helpful to you, feel free to leave a comment or send me a question! You can, of course, read more about configparser on Python’s documentation which has a much lengthier set of examples.