NullType Sentinels

2.3.1 · maintenance · verified Sat Apr 11

nulltype is a Python library (current version 2.3.1) that provides custom null values and sentinels, distinct from Python's built-in `None`, `False`, or `True`. It helps represent different states of 'emptiness' or 'undefined' values, such as `Passthrough`, `Prohibited`, or `Undefined`, without overloading standard Python nullish objects. The library aims to simplify code by allowing robust handling of potentially missing data in a consistent way. The last release was in June 2018, indicating a maintenance phase with infrequent updates.

Warnings

gotcha NullType instances are intended to be singletons (one per program) but their uniqueness is not strictly enforced. While this is rarely an issue in practice, users should be mindful that multiple instances with the same name could technically exist if not careful with usage patterns.
Fix: Rely on the convention of creating each NullType once, typically at module level, to ensure single instance behavior.
gotcha The library was last released in 2018 and was explicitly tested up to Python 3.7 pre-release. While generally compatible with newer Python versions, it is not actively tested against Python 3.8+ versions. Users on recent Python versions should verify compatibility, especially concerning subtle changes in built-in behaviors or type hinting.
Fix: Test your application's usage of `nulltype` thoroughly when upgrading to newer Python environments. Consider alternatives if explicit compatibility with the latest Python features or type hinting is critical.

Install

pip install nulltype Install stable version

Imports

NullType
```
from nulltype import NullType
```
Empty
```
from nulltype import Empty
```
Null
```
from nulltype import Null
```
Nothing
```
from nulltype import Nothing
```

Quickstart

Demonstrates how to create a custom `NullType` and its behavior when subjected to common Python operations (boolean evaluation, length, iteration, attribute access, item access, and calls). It also shows the use of the pre-defined `Empty`, `Nothing`, and `Null` sentinels.

from nulltype import NullType, Empty, Nothing, Null

# Create a custom null type
Undefined = NullType('Undefined')

# Test common Pythonic behaviors
assert bool(Undefined) is False
assert len(Undefined) == 0
assert list(Undefined) == []

# Accessing attributes, items, or calling a NullType instance
# By default, for custom NullTypes, attribute/call access returns Empty, and item access returns Nothing.
# For predefined sentinels like Empty, these operations return themselves.
assert Undefined.some_attribute is Empty
assert Undefined[22] is Nothing
assert Undefined("hey", 12) is Empty

# Using pre-defined sentinels
assert Empty.any_attr is Empty
assert Nothing[0] is Nothing
assert Null() is Null

print("NullType examples ran successfully!")

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