absence 1.1.1
Sentinel for absent values.
Requires Python: >=3.10

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*******************************************************************************
                                    absence                                    
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🕳️ A Python library package which provides a **sentinel for absent values** - a
falsey, immutable singleton that represents the absence of a value in contexts
where ``None`` or ``False`` may be valid values.


Key Features ⭐
===============================================================================

* 1️⃣  **Absence Sentinel**: A falsey singleton which represents absence.
* 🏭 **Absence Factory**: Create custom absence sentinels for package-specific
  or arbitrary needs.
* 𝒇 **Predicate Functions**: Determine if a value is absent.
* 🔍 **Type Support**: Type alias for optional values which may be absent.
  (Similar to ``typing.Optional`` and its relation to ``None``.)
* 🌟 **Builtins Integration**: Can install singleton and predicate function
  into Python builtins.


Installation 📦
===============================================================================

::

    pip install absence


Examples 💡
===============================================================================

Use the ``absent`` sentinel to represent missing values:

>>> from dataclasses import dataclass
>>> from absence import absent, is_absent, Absential
>>> @dataclass
... class User:
...     name: str | None
...     email: str | None
>>> def apply_partial_update(
...     user: User,
...     name: Absential[ str | None ] = absent,
...     email: Absential[ str | None ] = absent,
... ) -> User:
...     ''' Updates user fields if values provided.
...
...         Absent value means "don't change".
...         None value means "clear field".
...     '''
...     if not is_absent( name ): user.name = name
...     if not is_absent( email ): user.email = email
...     return user
>>> user = User( name = 'Alice', email = 'alice@example.com' )
>>> # Clear name but leave email unchanged
>>> updated = apply_partial_update( user, name = None )
>>> updated.name  # Cleared to None
>>> updated.email  # Unchanged
'alice@example.com'
>>> # Update both fields
>>> updated = apply_partial_update( user, name = 'Bob', email = 'bob@example.com' )
>>> updated.name
'Bob'
>>> updated.email
'bob@example.com'

Create package-specific absence sentinels:

>>> from absence import AbsenceFactory
>>> MISSING = AbsenceFactory( )
>>> bool( MISSING )
False


Use Cases 🎯
===============================================================================

* 🔄 **Optional Arguments**: When ``None`` is a valid argument value but you
  need to detect absence.
* 🎯 **Sentinel Values**: When you need a unique, falsey object to represent
  missing or invalid states.
* 🧩 **Type Safety**: When you want explicit typing for values that may be
  absent.


Comparison with Alternatives 🤔
===============================================================================

+-------------------------+----------+---------+------------+------------+
| Alternative             | Truthy?  | Unique? | Picklable? | Scope      |
+=========================+==========+=========+============+============+
| ``object()``            | Yes      | Yes     | No         | Arbitrary  |
+-------------------------+----------+---------+------------+------------+
| PEP 661 Sentinels       | Optional | Yes     | Yes        | Per-Module |
+-------------------------+----------+---------+------------+------------+
| ``dataclasses.MISSING`` | Yes      | Yes     | No         | Global     |
+-------------------------+----------+---------+------------+------------+
| ``typing.NoDefault``    | Yes      | Yes     | Yes        | Global     |
+-------------------------+----------+---------+------------+------------+
| ``absence.absent``      | No       | Yes     | No         | Global     |
+-------------------------+----------+---------+------------+------------+

The ``absent`` sentinel combines falsey behavior with global uniqueness,
making it particularly suitable for representing missing values in contexts
where ``None`` might be a valid value. The companion ``AbsenceFactory``
allows creation of arbitrary absence sentinels, when needed, such as for
specific packages.

See `PEP 661 ("Sentinel Values") <https://peps.python.org/pep-0661/>`_,
`typing.NoDefault
<https://docs.python.org/3/library/typing.html#typing.NoDefault>`_, and
`dataclasses.MISSING
<https://docs.python.org/3/library/dataclasses.html#dataclasses.MISSING>`_ for
more details on alternatives.


`More Flair <https://www.imdb.com/title/tt0151804/characters/nm0431918>`_
===============================================================================

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Other Projects by This Author 🌟
===============================================================================


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* `python-falsifier <https://github.com/emcd/python-falsifier>`_ (`falsifier <https://pypi.org/project/falsifier/>`_ on PyPI) 

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