base-typed-int 0.1.2

Strict typed integer base class with exact runtime subtype preservation and optional Pydantic v2 support.

base-typed-int

base_typed_int is a small Python library for building domain-specific integer types that remain real int objects at runtime.

Strict typed integer base class with exact runtime subtype preservation and optional Pydantic v2 support.

Why

BaseTypedInt helps model domain integers as explicit runtime types without losing normal int behavior.

Example use cases:

• UserAge
• RetryCount
• OrderPosition
• PriorityLevel
• ShardNumber

This library is designed for cases where plain int is too generic, but a full wrapper object would add unnecessary ceremony and runtime overhead.

Design goals

• exact runtime subtype is preserved
• behaves like plain int in normal arithmetic operations
• arithmetic operations usually return plain int
• subtype is preserved in containers, attributes, pickle, and Pydantic model fields
• Pydantic serialization exports plain integers
• strict input validation
• bool is explicitly rejected
• no extra public API beyond the integer value itself

Installation

Core

pip install base-typed-int

With Pydantic v2 support

pip install "base-typed-int[pydantic]"

Development

pip install "base-typed-int[dev]"

Quick start

from base_typed_int import BaseTypedInt

class UserAge(BaseTypedInt):
    pass

class Account:
    def __init__(self, user_age: UserAge) -> None:
        self.user_age: UserAge = user_age


user_age: UserAge = UserAge(18)

assert user_age == 18
assert isinstance(user_age, int)
assert isinstance(user_age, UserAge)
assert type(user_age) is UserAge
assert repr(user_age) == "UserAge(18)"

account: Account = Account(user_age=user_age)
assert account.user_age is user_age

Constructor behavior

The constructor is typed as accepting int, while still keeping a runtime validation guard for invalid non-integer inputs crossing dynamic boundaries.

from base_typed_int import BaseTypedInt

class RetryCount(BaseTypedInt):
    pass


value_from_int: RetryCount = RetryCount(3)
value_from_typed_int: RetryCount = RetryCount(RetryCount(3))

Invalid input raises BaseTypedIntInvalidInputValueError.

from base_typed_int import (
    BaseTypedInt,
    BaseTypedIntInvalidInputValueError,
)

class RetryCount(BaseTypedInt):
    pass

try:
    RetryCount("3")
except BaseTypedIntInvalidInputValueError:
    pass

try:
    RetryCount(True)
except BaseTypedIntInvalidInputValueError:
    pass

Why bool is rejected

In Python, bool is a subclass of int.

assert isinstance(True, int)
assert int(True) == 1

That behavior is useful in Python internals, but usually unsafe for domain modeling. A domain integer such as RetryCount, UserAge, or ShardNumber should not silently accept True or False.

For that reason, BaseTypedInt explicitly rejects bool even though bool is technically an int subtype.

Runtime behavior

Normal arithmetic keeps standard Python int semantics.

from base_typed_int import BaseTypedInt

class UserAge(BaseTypedInt):
    pass


user_age: UserAge = UserAge(18)

incremented_value: int = user_age + 1
multiplied_value: int = user_age * 2
subtracted_value: int = user_age - 3

assert incremented_value == 19
assert multiplied_value == 36
assert subtracted_value == 15

assert type(incremented_value) is int
assert type(multiplied_value) is int
assert type(subtracted_value) is int

This is intentional. The typed subtype marks the boundary value itself, while regular numeric operations stay native and unsurprising.

Containers and attributes

The exact subtype instance is preserved when stored and retrieved.

from base_typed_int import BaseTypedInt

class UserAge(BaseTypedInt):
    pass


class Account:
    def __init__(self, user_age: UserAge) -> None:
        self.user_age: UserAge = user_age


source_user_age: UserAge = UserAge(18)

user_age_list: list[UserAge] = [source_user_age]
user_age_by_field_name: dict[str, UserAge] = {
    "user_age": source_user_age,
}
values_by_user_age: dict[int, str] = {
    source_user_age: "present",
}
account: Account = Account(user_age=source_user_age)

assert user_age_list[0] is source_user_age
assert user_age_by_field_name["user_age"] is source_user_age
assert account.user_age is source_user_age
assert values_by_user_age[source_user_age] == "present"
assert values_by_user_age[18] == "present"
assert type(tuple(values_by_user_age.keys())[0]) is UserAge

Pickle support

Pickle roundtrip preserves the exact subtype.

import pickle

from base_typed_int import BaseTypedInt

class RetryCount(BaseTypedInt):
    pass


source_value: RetryCount = RetryCount(7)
serialized_value: bytes = pickle.dumps(source_value)
restored_value: object = pickle.loads(serialized_value)

assert restored_value == 7
assert isinstance(restored_value, RetryCount)
assert type(restored_value) is RetryCount

JSON behavior

Since BaseTypedInt inherits from int, standard JSON serialization naturally produces plain JSON numbers.

import json

from base_typed_int import BaseTypedInt

class RetryCount(BaseTypedInt):
    pass


value: RetryCount = RetryCount(7)
serialized_value: str = json.dumps(value)
restored_value: object = json.loads(serialized_value)

assert serialized_value == "7"
assert restored_value == 7
assert type(restored_value) is int

Pydantic v2 support

BaseTypedInt integrates with Pydantic v2 through __get_pydantic_core_schema__.

Validation rules:

• accepts only strict integer input
• rejects bool
• rejects strings and other non-integer values
• reconstructs the exact runtime subtype

Serialization rules:

• model_dump() returns plain integers
• model_dump_json() returns JSON numbers

Example

from pydantic import BaseModel

from base_typed_int import BaseTypedInt

class RetryCount(BaseTypedInt):
    pass


class MetricsModel(BaseModel):
    primary_retry_count: RetryCount
    backup_retry_count: RetryCount


metrics_model: MetricsModel = MetricsModel.model_validate(
    {
        "primary_retry_count": 5,
        "backup_retry_count": 8,
    }
)

assert type(metrics_model.primary_retry_count) is RetryCount
assert type(metrics_model.backup_retry_count) is RetryCount

python_dump: dict[str, object] = metrics_model.model_dump()
json_dump: str = metrics_model.model_dump_json()

assert python_dump == {
    "primary_retry_count": 5,
    "backup_retry_count": 8,
}
assert json_dump == '{"primary_retry_count":5,"backup_retry_count":8}'

Roundtrip from exported payload

source_model: MetricsModel = MetricsModel.model_validate(
    {
        "primary_retry_count": 5,
        "backup_retry_count": 8,
    }
)

python_dump: dict[str, object] = source_model.model_dump()
restored_model: MetricsModel = MetricsModel.model_validate(python_dump)

assert type(restored_model.primary_retry_count) is RetryCount
assert type(restored_model.backup_retry_count) is RetryCount

Error types

from base_typed_int import (
    BaseTypedIntError,
    BaseTypedIntInvalidInputValueError,
    BaseTypedIntInvariantViolationError,
)

• BaseTypedIntError — root exception for library errors
• BaseTypedIntInvalidInputValueError — invalid caller input
• BaseTypedIntInvariantViolationError — internal invariant or integration failure

Testing

pytest

With coverage:

pytest --cov=base_typed_int --cov-report=term-missing

Type checking

mypy src tests
pyright

Linting

ruff check .
ruff format .

Build

python -m build

Package structure

src/
  base_typed_int/
    __init__.py
    _base_typed_int.py
    _exceptions.py
    py.typed

Compatibility

• Python 3.10+
• CPython
• Pydantic v2 support is optional

Notes

BaseTypedInt is intentionally minimal. It is not a numeric validation framework and does not enforce domain-specific constraints such as non-negative values, ranges, or upper bounds.

Those constraints should be modeled in your own subclasses or service-layer validation where appropriate.

License

MIT