constantly

library23.10.4pypypi✓ verified 24d ago

constantly is a Python library providing symbolic constants, particularly useful for creating enumerated types and immutable values that are easily comparable by identity. It is maintained by the Twisted project, with releases appearing periodically. The current version is 23.10.4.

type-stubs

pip install constantly

github ↗package ↗

INSTALL

IMPORT

SIG · CONSTANTLY

constantly

type-stubspythonv23.10.4

Install

1.5s avg

Import

10ms

Disk

16MB

Pass rate

10/ 10

Env Coverage10 / 10

glibc

3.9–3.13

musl

3.9–3.13

Install & Compatibility

Where this runs

tested against v23.10.4 · pip install

no network on importno background threads

Install × environment matrix

Each cell = how many times install + import succeeded across repeated harness runs. Partial = flaky.
glibc = Debian/Ubuntu slim · musl = Alpine Linux

musl

py 3.10–3.95 runs

installs and imports cleanly · install 0.0s · import 0.010s · 17.9MB

glibc

py 3.10–3.95 runs

installs and imports cleanly · install 1.5s · import 0.006s · 18MB

16MB installed

● package 16MB

Code

Verified usage

Verified import paths — ran on the pinned version, not inferred.

FlagConstant

✓ from constantly import FlagConstant

✗ from constantly import Constant

Flags

✓ from constantly import Flags

✗ from constantly import Constant

NamedConstant

✓ from constantly import NamedConstant

✗ from constantly import Constant

This example demonstrates how to define a set of named constants using `Values` and `NamedConstant`, and how to access and compare them. `NamedConstant` instances within a `Values` class are singletons.

from constantly import NamedConstant, Values class Fruit(Values): apple = NamedConstant() banana = NamedConstant() orange = NamedConstant() # Accessing constants print(f"Apple constant: {Fruit.apple}") print(f"Apple name: {Fruit.apple.name}") print(f"Apple value: {Fruit.apple.value}") # Comparing constants by identity (preferred) print(f"Is Fruit.apple the same object as Fruit.apple? {Fruit.apple is Fruit.apple}") print(f"Is Fruit.apple the same object as Fruit.banana? {Fruit.apple is Fruit.banana}") # Iterating over constants in the class print("All fruits:") for fruit in Fruit.iterconstants(): print(f"- {fruit.name}")

Debug

Known issues

breakingPython 3.7 support was dropped in `constantly` version 23.10.0.

fix

Ensure your environment uses Python 3.8 or newer. If you need Python 3.7 support, pin `constantly<23.10.0`.

affects: >=23.10.0

gotchaNamedConstants defined within a `Values` class are singletons. Prefer identity comparison (`is`) over value comparison (`==`) for correctness, especially when comparing against other objects or similar strings.

fix

Always use `constant_a is constant_b` for comparing two `NamedConstant` instances. While `==` works for comparing a `NamedConstant` to its string name, `is` ensures you're comparing the exact symbolic object.

affects: all

gotchaAttempting to modify the `name` or `value` attributes of a `Constant` or `NamedConstant` after definition will result in an `AttributeError`, as they are designed to be immutable.

fix

Constants are immutable by design. Define them once and treat them as fixed values throughout your application.

affects: all

breakingAccessing a `NamedConstant` or `Constant` instance that was not properly registered with its `Values` container can lead to an `AttributeError: 'NoneType' object has no attribute '__name__'` when its `__repr__` method is called. This typically happens if the constant's `_container` attribute is `None`.

fix

Ensure all `NamedConstant` and `Constant` instances are defined *within* a `Values` class or properly assigned to their `_container` if created dynamically. Misconfiguration or incorrect usage of the library's `Values` class can result in unassigned containers. For example, if defining constants dynamically, explicitly set the `_container` attribute to the `Values` instance.

affects: all

breakingAttempting to represent (e.g., `print` or `repr()`) a `NamedConstant` instance whose internal `_container` attribute is `None` will result in an `AttributeError: 'NoneType' object has no attribute '__name__'`.

fix

Ensure all `NamedConstant` instances are defined as class attributes within a `constantly.Values` subclass. This allows the `ValuesMetaClass` to correctly set the `_container` attribute for each constant. If you instantiate `NamedConstant` directly, its default `__repr__` will fail unless `_container` is manually set or a custom `__repr__` is provided.

affects: all

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Version history

23.10.4latest on PyPI · released Oct 28, 2023

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Dependencies

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Agent activity

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Resources

githubhttps://github.com/twisted/constantly ↗

packagehttps://pypi.org/project/constantly/ ↗