Optional Values Example (optional_values.py)

Purpose

Demonstrates nullable / optional configuration patterns:

• optional=True shorthand vs Optional(...) wrapper
• Optional enums, strings, integers
• Empty string vs None semantics
• Cascading defaults & fallback logic

Running

uv run python examples/optional_values.py

Generated config.ini (Excerpt)

First run (only defaults materialize):

[OptionalConfig]
database_url = sqlite:///app.db
log_file = app.log
worker_count = 4
optional_string = default
optional_int = 42
optional_enum = dev
api_key = 
secret_key = 

[DatabaseConfig]
connection_string = sqlite:///fallback.db
username = 
password = 
port = 5432

After code mutates values or sets some to None, lines representing None are removed (or may remain absent if never set). When assigning new values, those lines reappear.

Example after updates:

[OptionalConfig]
database_url = 
log_file = 
worker_count = 
optional_string = new value
optional_int = 100
optional_enum = prod
api_key = 
secret_key = 

[DatabaseConfig]
connection_string = postgresql://localhost/mydb
username = admin
password = 
port = 5433

Notes

• Setting a value to None for an optional field removes it from the config file.
• Empty string "" is distinct from None (still persisted as a blank value).
• Use fallback logic in application code (see get_connection_params).

Try Variations

• Remove the whole [DatabaseConfig] section and re-run.
• Set worker_count = None then reassign an integer.