Flask

pip install "errium[flask]"

Integration

from flask import Flask
from errium_flask import ErriumFlask

app = Flask(__name__)
ErriumFlask(app)

That single call is the whole integration. It registers one error handler against the base Exception class:

app.register_error_handler(Exception, self._handle_exception)

Registering on Exception is sufficient because Flask dispatches both raised HTTPExceptions — from flask.abort(), say — and unhandled generic exceptions to it when no more specific handler exists.

The extension also takes classifiers=[...] (added to the default engine) and engine= (replaces it) — see custom classifiers. It adds a before_request hook that assigns the request’s trace id, available as flask.g.errium_trace_id.

App factory pattern

If you build your app with a factory, construct the extension first and attach it later:

from errium_flask import ErriumFlask

errium = ErriumFlask()

from flask import Flask
from .extensions import errium

def create_app():
    app = Flask(__name__)
    errium.init_app(app)
    return app

What gets caught

errium_flask ships WerkzeugHTTPExceptionClassifier at priority 200, which matches any Werkzeug HTTPException, maps exc.code through the shared status-code table, and uses exc.description as the message. An exception with no code falls back to 500.

Protocol headers on the exception are kept: Werkzeug’s TooManyRequests(retry_after=30) produces Retry-After: 30, and a 405 carries Allow. Every error response also has an X-Trace-Id header.

Uncaught exceptions of any other type reach GenericExceptionClassifier and return INTERNAL_SERVER_ERROR.

Validation errors

Flask has no request-validation exception type of its own, so there is nothing equivalent to FastAPI’s RequestValidationError to hook. Instead, the handler checks whether the caught exception is a pydantic ValidationError and, if it is, runs it through ValidationNormalizer to produce the same flat details map the other adapters emit.