python 41 lines · 8 steps

Layered INI config loading in Python

A small toolkit that loads INI files, merges section defaults, and extracts typed database settings.

Explained by highlit
Intermediate configuration parsing defaults type-coercion layering
1from configparser import ConfigParser, ExtendedInterpolation
2from pathlib import Path
3 
4 
5def load_config(*paths, defaults=None):
6 parser = ConfigParser(
7 interpolation=ExtendedInterpolation(),
8 default_section="defaults",
9 )
10 if defaults:
11 parser.read_dict({"defaults": defaults})
12 
13 read = parser.read([Path(p) for p in paths], encoding="utf-8")
14 if not read:
15 raise FileNotFoundError(f"no config files found among {paths!r}")
16 
17 return parser
18 
19 
20def merged_section(parser, section, base="common"):
21 if not parser.has_section(section):
22 raise KeyError(f"missing section [{section}]")
23 
24 result = {}
25 if parser.has_section(base):
26 result.update(parser[base])
27 result.update(parser[section])
28 return result
29 
30 
31def database_settings(parser, env):
32 section = merged_section(parser, f"db.{env}", base="db.common")
33 return {
34 "host": section.get("host", "localhost"),
35 "port": section.getint("port", fallback=5432) if hasattr(section, "getint") else int(section.get("port", 5432)),
36 "name": section["name"],
37 "user": section["user"],
38 "password": section.get("password", ""),
39 "pool_size": int(section.get("pool_size", 5)),
40 "ssl": section.get("ssl", "false").lower() in ("1", "true", "yes"),
41 }
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STEP 01

Walkthrough

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Three takeaways
  1. 1ExtendedInterpolation plus a default section lets INI files reference and inherit values without repetition.
  2. 2Merging a base section under a specific one gives you clean layered overrides from flat config files.
  3. 3Config values are always strings, so coerce and default them explicitly when you read them out.

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