ktx - Shared context library

Introduction

ktx is a Context library aimed to simplify a process of creating and managing shared data in Python.

Quick example:

from ktx.simple import SimpleContext

ctx = SimpleContext()
ctx.data.some_attribute = "value1"

You may also set created Context object as current for current thread or asyncio.Task:

from ktx import ctx_wrap, get_current_ctx
from ktx.simple import SimpleContext

with ctx_wrap(SimpleContext()) as ctx:
    ctx.data.some_attribute = "value1"

    ctx2 = get_current_ctx()
    assert ctx2 is ctx

But also (thanks for ContextVar) context is available in any place of current coroutine in asyncio-world (note that asyncio-context is copied in the creating of new tasks):

import asyncio

from ktx import get_current_ctx
from ktx.simple import SimpleContext


async def f1():
    ctx = get_current_ctx()
    assert ctx.get("some_attribute") == "value1"


async def main():
    with SimpleContext() as ctx:
        ctx.data.some_attribute = "value1"
        task1 = asyncio.create_task(f1())
        await asyncio.sleep(1)

    await task1

There exists an abstract interface (Protocol) for any "kind of Contex", so you may implement your own Context classes by implementing ktx.abc.Context protocol:

API

Context provides the following methods:

• set(key: str, value: Any) -> Any: set value by key
• get(key: str) -> Any: get value by key
• get_data() -> Mapping[str, Any]: get all shared data
• get_user() -> ContextUser: get user object
• uq_id() -> str: get unique id of context

Data Inheritance

This is best described using the following snippet:

from ktx import ctx_wrap
from ktx.simple import SimpleContext

with ctx_wrap(SimpleContext()) as parent_ctx:
    parent_ctx.data.attr1 = "val1"
    parent_ctx.data.attr2 = "val2"

    with ctx_wrap(SimpleContext()) as child_ctx:
        assert child_ctx.data.attr1 == "val1"
        assert child_ctx.data.attr2 == "val2"

        child_ctx.data.attr2 = "val3"
        assert child_ctx.data.attr2 == "val3"

    assert parent_ctx.data.attr2 == "val2"

Logging

Structlog

There is a helper function ktx.log.ktx_add_log useful for structlog processors that propagates all Context-specific attributes to a logging event dict.

Custom context

It is possible to define a custom Context class in order to better support strong typing. You would need to implement ktx.abc.Context protocol and then you may use it with ctx_wrap functions as usual.

Note that you would need to implement general get() and set() methods for arbitrary fields as they may be accessed by other libraries which are using Context.

And the get_data() method must return all shared data of this context so it will be available during logging. For example:

from typing import Mapping, Any

from ktx.user import ContextUser
from ktx.abc import Context


class MyContext(Context):  # Note that inheritance is not required.
    def __init__(self, uq_id: str, *, custom_field: str):
        self.custom_field = custom_field

        self._uq_id = uq_id
        self._data: dict[str, Any] = {}
        self._user = ContextUser()

    def uq_id(self) -> str:
        return self._uq_id

    def get_data(self) -> Mapping[str, Any]:
        return {
            **self._data,
            "custom_field": self.custom_field,
        }

    def get_user(self) -> ContextUser:
        return self._user

    def get(self, key: str) -> Any:
        return self._data.get(key)

    def set(self, key: str, value: Any):
        self._data[key] = value

And then you may use this MyContext in safe manner like this:

from ktx import ctx_wrap, get_current_ctx

with ctx_wrap(MyContext()) as ctx:
    ctx.custom_field = "value1"

    assert get_current_ctx(MyContext) is ctx