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Python Constants Best Practices

Satellite · Variables

Python Constants

Use uppercase naming, module scoping, and typing helpers to treat values as constants even without language-level enforcement.

See conventionsLock them with typing

Conventions​

MAX_RETRIES = 3
API_BASE_URL = "https://api.example.com"
  • Define constants at module level.
  • Use uppercase snake case.
  • Group related constants in dedicated modules (e.g., settings.py).

Typing enforcement​

from typing import Final

MAX_CONNECTIONS: Final = 100

Static analyzers (mypy, pyright) flag reassignment when using Final.

Runtime strategies​

  • Avoid reassigning constants by convention.
  • Use dataclasses.dataclass(frozen=True) or NamedTuple for grouped read-only data.
  • For configuration, load from environment variables once and expose as constants.

Next up in your learning path

Variable fundamentals

See how constants relate to regular variables.

Companion

Type hints

Document constants with typing.

Reference

Modules & packages

Organize constants into modules cleanly.

Structure