dagger/dagger · error · ObjectNotFoundError

Main object with name '{self._main_name}' not found or class

Error message

Main object with name '{self._main_name}' not found or class not decorated with '@dagger.object_type'
If you believe the module name '{MODULE_NAME}' is incorrectly being converted into PascalCase, please file a bug report.

What it means

The module's main object (module name converted to PascalCase) must correspond to a class decorated with @dagger.object_type in the registered objects map. If get_object(main_name) raises ObjectNotFoundError, _typedefs re-raises with guidance: either the class is missing the decorator or the PascalCase conversion of MODULE_NAME doesn't match the class name.

Source

Thrown at sdk/python/src/dagger/mod/_module.py:139

            output = json.dumps(result)
        except TypeError as e:
            raise RegistrationError(str(e), e) from e
        await anyio.Path(TYPE_DEF_FILE).write_text(output)

    async def _typedefs(self) -> str:  # noqa: C901, PLR0912, PLR0915
        if not self._main_name:
            msg = "Main object name can't be empty"
            raise ValueError(msg)
        try:
            self.get_object(self._main_name)
        except ObjectNotFoundError as e:
            msg = (
                f"Main object with name '{self._main_name}' not found or class not "
                "decorated with '@dagger.object_type'\n"
                f"If you believe the module name '{MODULE_NAME}' is incorrectly "
                "being converted into PascalCase, please file a bug report."
            )
            raise ObjectNotFoundError(msg, extra=e.extra) from None

        mod = dag.module()

        # Object types
        for obj_name, obj_type in self._objects.items():
            if self.is_main(obj_type):
                # Only the main object's constructor is needed.
                # It's the entrypoint to the module.
                obj_type.get_constructor(self._converter)

                # Module description from main object's parent module
                if desc := get_parent_module_doc(obj_type.cls):
                    mod = mod.with_description(desc)

            # Object/interface type
            type_def = dag.type_def()
            if obj_type.interface:
                type_def = type_def.with_interface(

View on GitHub (pinned to 82ba2681db)

Solutions

1. Ensure a class named exactly PascalCase(your-module-name) exists and is decorated with @dagger.object_type (e.g. module 'my-mod' -> class MyMod).
2. If the desired class name differs, rename the module directory or the class so they correspond.
3. Verify the module's __init__.py imports the main class so it's registered.
4. If PascalCase conversion is wrong (e.g. digits/acronyms), file a bug report with the SDK as the message suggests.

Example fix

// before
# src/my_mod/__init__.py
class MyModule:  # no decorator, wrong name for 'my-mod'
    pass

// after
import dagger

@dagger.object_type
class MyMod:
    ...

import re

module_name = "my-mod"  # from dagger.json
expected = "".join(p.capitalize() for p in re.split(r"[-_]", module_name))
# ensure a class with this exact name exists and is decorated:
# @dagger.object_type
# class MyMod: ...
assert any(name == expected for name in globals()), f"missing main object class {expected}"

def has_main_object(module_name: str, objects: dict) -> bool:
    pascal = "".join(p.capitalize() for p in re.split(r"[-_]", module_name))
    return pascal in objects

try:
    await module.register()
except ObjectNotFoundError as e:
    logger.error("main object missing: %s", e)
    raise SystemExit(1) from e

When it happens

Trigger: Running a Python Dagger module where no class named PascalCase(module_name) exists, or it exists but lacks @dagger.object_type; renaming the module directory without renaming the main class; main class defined in a file not imported by the entrypoint.

Common situations: Renaming a module (e.g. dir 'my-mod' requires class 'MyMod'); a typo'd class name; moving the main object into another module without updating names; forgetting the decorator after refactoring.

Related errors

• {str(e)}
• Seems like the SDK module isn't registering the types correc
• struct types must be named
• unsupported {context}: {typ.hint!r}
• Failed to serialize final result as JSON: {e}

AI-assisted analysis of dagger/dagger@82ba2681db (2026-09-05). Data as JSON: /api/errors/c1390515d4d8c3c2. Report an issue: GitHub.