Explain INI code

What this INI sample shows

sections and keys

[server] starts a section, and each name = value line below it belongs to that section until the next one. A line starting with ; is a comment. Python's configparser listed the sections as ['server', 'database', 'email']: [DEFAULT] isn't listed, because it's special.

[DEFAULT]

Every section can see the keys in [DEFAULT], unless it sets its own. [email] has no debug line, so it got the default no, read as False; [server] sets debug = yes and read as True. [email] also had log_dir without ever naming it.

%(name)s values

%(log_dir)s is filled in from another key, here the one in [DEFAULT]. backup_file came out as /var/log/invoicer/backup.log.

everything is text

Every value is read as text: port came back as the string '8080'. getint, getfloat and getboolean convert it, and getboolean took yes and no. Key names don't care about case, so PORT found port, but section names do: there was no SERVER section.

Good to know

• Read with configparser in Python 3.14. Other programs that read .ini files may follow different rules, so check the docs of the one reading yours.
• A % in a value has to be written %%. With password = 50%off, reading it raised InterpolationSyntaxError: '%' must be followed by '%' or '(', found: '%off'. ConfigParser(interpolation=None) read it as 50%off.
• A missing file isn't an error: read("nope.ini") returned [] and there were no sections. Check what read returns.
• The same key twice in one section stopped the read with DuplicateOptionError.

Watch out: A comment at the end of a line becomes part of the value. port = 8080 ; dev only read as '8080 ; dev only', and getint failed with ValueError: invalid literal for int() with base 10: '8080 ; dev only'. Put comments on their own line, or pass inline_comment_prefixes=(";",), which read it as '8080'.