Docs: decimal.BasicContext etc. are not classes

[Feuermurmel]

Documentation

The decimal module exports three constants BasicContext, ExtendedContext and DefaultContext, which are instances of Context:

$ python3
Python 3.13.1 (main, Dec 20 2024, 10:15:12) [Clang 14.0.0 (clang-1400.0.29.202)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import decimal
>>> type(decimal.BasicContext)
<class 'decimal.Context'>

The documentation of module decimal is misleading by containing these 3 declarations:

class decimal.BasicContext
        ...

class decimal.ExtendedContext
        ...

class decimal.DefaultContext
        ...

This made me think that these are subclasses of Context that need to be instantiated like this:

>>> decimal.setcontext(decimal.ExtendedContext())
Traceback (most recent call last):
  File "<python-input-2>", line 1, in <module>
    decimal.setcontext(decimal.ExtendedContext())
                       ~~~~~~~~~~~~~~~~~~~~~~~^^
TypeError: 'decimal.Context' object is not callable

I would expect the declarations to look more like the ones e.g. under Rounding modes.

Linked PRs

• gh-128349: use .. data:: instead of .. class:: for pre-defined decimal Context objects #128379
• [3.13] gh-128349: Use .. data:: instead of .. class:: for pre-defined decimal Context objects (GH-128379) #128401
• [3.12] gh-128349: Use .. data:: instead of .. class:: for pre-defined decimal Context objects (GH-128379) #128402

[terryjreedy]

@rhettinger decimal expert

[skirpichev]

This looks as a bug for me, indeed:

>>> inspect.isclass(decimal.BasicContext)
False
>>> inspect.isclass(decimal.Context)
True

BTW, in the sphinx docs BasicContext referenced with const prefix.

[picnixz]

We should change .. class:: into .. data:: (especially, if we are referencing them using the :const: role). Note that we say:

In addition to the three supplied contexts, new contexts can be created with the Context constructor.

So we should assume that these are not meant to be classes at all (if someone was wondering whether they could act as such)