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  7. Exceptions

Exceptions

Exceptions

The cloaca package defines no custom exception classes. There is no CloacaException, no WorkflowError, no TaskError, no DatabaseError — the bindings raise standard Python built-in exceptions, chosen by error category. Catch ValueError, KeyError, RuntimeError, and friends directly.

The CloacinaApiError class you may see in other Cloacina code belongs to the separate cloacina-client service SDK (pip install cloacina-client), not to cloaca. See the Python SDK reference.

Which built-in is raised when

Exception Raised by
ValueError Most validation and operational failures: invalid decorator arguments (@cloaca.task, @cloaca.trigger, @cloaca.constructor), WorkflowBuilder.add_task / build() / __exit__ failures (unknown task, cycle, validation), invalid DefaultRunnerConfig values, DefaultRunner.with_schema given a non-PostgreSQL URL or a bad schema name, and every DefaultRunner operation that the runtime rejects — execute() on an unknown workflow, an invalid cron expression in register_cron_workflow, unknown schedule/trigger ids, and so on
KeyError cloaca.var(name) when CLOACINA_VAR_<name> is unset; Context.update(), context[key], and del context[key] on a missing key; Context.secret() / secret_field() when the secret or field does not exist
RuntimeError DefaultRunner / DatabaseAdmin construction failures (bad URL, connection or migration failure, runtime thread died); DatabaseAdmin.create_tenant / remove_tenant failures; Context.secret() when no secret resolver is configured (CLOACINA_SECRET_KEK unset) or the secrets backend fails
PermissionError Context.secret() / secret_field() when the secret exists but is not granted to the workflow
TypeError Wrong argument types passed to binding functions (for example a non-dict where a dict is required)
AttributeError ComputationGraphBuilder exit when the topology references a node name with no matching @cloaca.node function

Source: crates/cloacina-python/src — the crate contains no create_exception! invocations; every error path maps onto one of the built-ins above (see context.rs, bindings/runner.rs, bindings/admin.rs, computation_graph.rs, loader.rs).

Task failures are results, not exceptions

An exception raised inside a task body fails that task; the workflow engine records the failure (and applies the task’s retry policy) rather than propagating the exception to the caller of runner.execute(). Inspect the returned WorkflowResult instead:

import cloaca

runner = cloaca.DefaultRunner("sqlite:///app.db")
result = runner.execute("my_workflow", cloaca.Context())

if result.status != "Completed":
    print(f"Workflow failed: {result.error_message}")

Handling errors 

import cloaca

# Construction errors: RuntimeError
try:
    runner = cloaca.DefaultRunner("postgresql://user:pass@nonexistent:5432/db")
except RuntimeError as e:
    print(f"Could not start runner: {e}")

# Operational errors: ValueError
try:
    result = runner.execute("nonexistent_workflow", cloaca.Context())
except ValueError as e:
    print(f"Execution rejected: {e}")

try:
    runner.register_cron_workflow("daily_report", "not a cron expr", "UTC")
except ValueError as e:
    print(f"Invalid cron expression: {e}")

# Variable registry: KeyError
try:
    url = cloaca.var("DATABASE_URL")   # reads CLOACINA_VAR_DATABASE_URL
except KeyError:
    url = "sqlite:///default.db"

Because the categories are built-ins, standard Python patterns apply — there is no package-specific base class to catch. If you need a catch-all around a cloaca call, catch Exception and inspect the message.

Service-client errors (cloacina-client, not cloaca)

Code that talks to a running cloacina-server over HTTP uses the separate cloacina-client SDK, whose typed error does exist:

from cloacina_client import Client, CloacinaApiError

client = Client("http://localhost:8080", api_key="...")
try:
    client.get_workflow("missing")
except CloacinaApiError as e:
    print(e.status, e.code, e.message)   # 404 workflow_not_found ...

CloacinaApiError carries the canonical {error, code} envelope (clients/python/src/cloacina_client/_client.py). It is never raised by cloaca.

See Also

gdoc_arrow_left_alt WorkflowResult Package Manifest gdoc_arrow_right_alt