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contextvars.ContextVar provides per-context (per-async-task or per-thread) state. AlexBerUtils provides two helpers for discovering all ContextVar instances in a module and resetting them to a known initial state.

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get_context_vars

Scans one or more modules for top-level ContextVar instances, pairs each one with a factory function that produces its default value, resets them all immediately, and returns the list of entity dicts. 
get_context_vars(*modules, factory_method_creator=None) -> List[dict]

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Parameters

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*modules
ModuleType
required
One or more Python module objects to scan. dir(module) is used to enumerate attributes; only those that are ContextVar instances are collected.
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factory_method_creator
Callable[[ContextVar, ModuleType], Callable]
Optional function that resolves the factory callable for a given ContextVar.Signature: (var: ContextVar, module: ModuleType) -> CallableDefault: looks for an attribute named <var.name>_DEFAULT on the same module as the ContextVar.
# Default resolution: if the ContextVar is named `request_id`,
# the factory is module.request_id_DEFAULT
factory_method_creator = lambda var, module: getattr(module, f"{var.name}_DEFAULT")

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Return value

A list of dicts, each with:
KeyTypeDescription
"var"ContextVarThe ContextVar instance.
"factory"CallableZero-argument callable that produces the default value.
get_context_vars calls reset_context_vars internally, so all discovered vars are reset to their defaults before the list is returned.
If no modules are passed, an empty list is returned immediately.

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Usage

import my_module
from alexber.utils.thread_locals import get_context_vars

# my_module must expose `request_id_DEFAULT` for a ContextVar named `request_id`
entities = get_context_vars(my_module)

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reset_context_vars

Resets every ContextVar in the entity list to its default value by calling its associated factory. 
reset_context_vars(*entities) -> None
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*entities
dict
required
Entity dicts as produced by get_context_vars. Each dict must have a "var" (ContextVar) and a "factory" (callable).
Raises ValueError if any factory is not callable. 
from alexber.utils.thread_locals import get_context_vars, reset_context_vars
import my_module

# Collect once at startup
entities = get_context_vars(my_module)

# Reset before each request / task
reset_context_vars(*entities)

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End-to-end example

This pattern is common in request-scoped or task-scoped applications where you want to ensure clean state at the start of every unit of work. 
# my_module.py
from contextvars import ContextVar

request_id: ContextVar[str] = ContextVar('request_id')
user_id: ContextVar[int] = ContextVar('user_id')

# Factories follow the `<name>_DEFAULT` convention
def request_id_DEFAULT() -> str:
    return ''

def user_id_DEFAULT() -> int:
    return 0

# app.py
import my_module
from alexber.utils.thread_locals import get_context_vars, reset_context_vars

# At startup: discover all ContextVars and reset them
entities = get_context_vars(my_module)

async def handle_request(req):
    # Reset to defaults at the start of each request
    reset_context_vars(*entities)

    my_module.request_id.set(req.id)
    my_module.user_id.set(req.user.id)

    await process(req)
Store the entities list returned by get_context_vars as a module-level variable and reuse it across requests. Calling get_context_vars repeatedly is wasteful because it rescans the module each time.
reset_context_vars modifies the ContextVar in the current context. In an async application each asyncio.Task has its own context copy, so resetting in one task does not affect others.

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