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Importing adcp.types.domains.formats first fails with a circular import (CanonicalFormatBase) #1784
Description
from adcp.types.domains.formats import Slot (or import adcp.types.domains.formats.canonical) raises ImportError when it is the first adcp types import in a process. It works only if something has already imported a model such as adcp.types.Product or adcp.types.Format. So a script, worker or test module that imports just the canonical-format types fails depending on import order, and adding or removing an unrelated import elsewhere can start or stop the failure.
Repro (9.3.0 and 10.0.0b4, fresh interpreter)
$ python -I -c "from adcp.types.domains.formats import Slot"
ImportError: cannot import name 'CanonicalFormatBase' from partially initialized module
'adcp.types.domains.formats.canonical._base' (most likely due to a circular import)
$ python -I -c "import adcp.types; from adcp.types.domains.formats import Slot"
ImportError: (same)
$ python -I -c "from adcp.types import Product; from adcp.types.domains.formats import Slot; print('ok')"
ok
The cycle:
adcp/types/domains/formats/__init__.py:19
-> formats/canonical/_base.py:14
-> core/__init__.py:207
-> core/async_response_data.py:11
-> creative/__init__.py:63
-> creative/list_creative_formats_response.py:17
-> core/format.py:23
-> formats/canonical/agent_placement.py:13 (from ._base import CanonicalFormatBase; _base is half-initialized)
Suggested fix
Break the cycle at canonical/_base.py. It should import the leaf modules it needs, not the adcp.types.domains.core package (whose __init__ pulls in every response union). Add a test that imports each public types package first, in a fresh interpreter.
Activity
fix(types): make the domain package roots lazy so a types package imp…
fix(types): make the domain package roots lazy so a types package imp…
fix(types): make the domain package roots lazy so a types package imp…
bokelley commentedon Nov 2, 2026
Fixed by #1797 on
next(squash8331c88d) and #1798 onmain(squash7447d00c): the domain package roots are lazy (PEP 562), sofrom adcp.types.domains.formats import Slotimports first in a fresh interpreter in any order.tests/test_domain_roots_import_in_any_order.pyimports every domain root first in a subprocess.