niltype: Singleton for Missing Values

1.0.2 · active · verified Fri Apr 17

A small Python library that provides a singleton `Nil` object. This object is designed to represent missing or unset values in scenarios where `None` is a valid and meaningful data value, thus avoiding ambiguity. Currently at version 1.0.2, it's a stable, single-purpose library with infrequent updates.

Common errors

```
AttributeError: 'NilType' object has no attribute 'some_property'
```
cause Attempting to access attributes or methods on a variable that holds `Nil` without first checking for its presence.

fix Always check `if my_var is not Nil:` before attempting to access properties or methods on `my_var`, as `Nil` has no user-defined attributes.
```
TypeError: can't concat NilType to str
```
cause Passing `Nil` directly to functions or operations that expect a specific data type (e.g., string concatenation, arithmetic operations, database queries) and do not explicitly handle `Nil`.

fix Implement explicit checks for `Nil` and handle it appropriately (e.g., return early, provide a default value, raise a more specific exception) before passing the variable to type-sensitive operations. For example: `my_str = 'Default' if my_var is Nil else str(my_var)`.

Warnings

gotcha The `Nil` object evaluates to `False` in a boolean context, similar to `None`, empty collections, or zero. However, `Nil` is not `None` (`Nil != None`).
Fix: Always use identity checks (`if obj is Nil:` or `if obj is not Nil:`) when specifically checking for the `Nil` singleton. Avoid `if not obj:` if you need to distinguish `Nil` from other falsey values.
gotcha `Nil` is a true singleton, meaning there is only one instance of it throughout your application's lifetime. Any variable assigned `Nil` will reference this single instance.
Fix: This is by design and fundamental to `niltype`. It implies `Nil` cannot carry state or attributes specific to a particular missing value context. If you need contextual information, wrap `Nil` in a custom class or use a different pattern.

Install

pip install niltype Install niltype

Imports

Nil
```
from niltype import Nil
```

Quickstart

Demonstrates how to import and use the `Nil` singleton to distinguish between a truly missing value (represented by `Nil`) and an intentional `None` value in a function's return, especially useful for API responses or configuration.

from niltype import Nil

def get_user_setting(user_id: int, setting_name: str):
    """Simulates fetching a user setting where Nil means 'not found'."""
    if user_id == 1:
        if setting_name == "theme":
            return "dark"
        elif setting_name == "timeout":
            return None # None is a valid timeout (e.g., no timeout)
    return Nil # Setting does not exist for this user

# Example usage:
setting = get_user_setting(1, "theme")
print(f"Theme setting: {setting} (is Nil: {setting is Nil})")

setting = get_user_setting(1, "timeout")
print(f"Timeout setting: {setting} (is Nil: {setting is Nil})")

setting = get_user_setting(2, "language")
print(f"Language setting: {setting} (is Nil: {setting is Nil})")

if setting is Nil:
    print("\nSetting 'language' for user 2 is missing.")
elif setting is None:
    print("\nSetting 'timeout' is explicitly set to None (no timeout).")
else:
    print(f"\nSetting is {setting}.")

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