locustio/locust · error · ImportError

deprecation_message (e.g. The Locust class has been renamed

Error message

deprecation_message (e.g. The Locust class has been renamed to User in version 1.0. Use User instead)

What it means

deprecated_locust_meta_class builds a metaclass that allows only its internal placeholder classes to be created; any subclass of a deprecated Locust/HttpLocust alias raises ImportError with the supplied deprecation message.

Source

Thrown at locust/util/deprecation.py:26

    from locust.user.task import TaskSet

    if "task_set" in class_dict:
        task_set = class_dict["task_set"]
        if issubclass(task_set, TaskSet) and not hasattr(task_set, "locust_task_weight"):
            warnings.warn(
                "Usage of User.task_set is deprecated since version 1.0. Set the tasks attribute instead "
                f"(tasks = [{task_set.__name__}])",
                DeprecationWarning,
            )


def deprecated_locust_meta_class(deprecation_message):
    class MetaClass(type):
        def __new__(mcs, classname, bases, class_dict):
            if classname in ["DeprecatedLocustClass", "DeprecatedHttpLocustClass", "DeprecatedFastHttpLocustClass"]:
                return super().__new__(mcs, classname, bases, class_dict)
            else:
                raise ImportError(deprecation_message)

    return MetaClass


# PEP 484 specifies "Generic metaclasses are not supported", see https://github.com/python/mypy/issues/3602, ignore typing errors
class DeprecatedLocustClass(
    metaclass=deprecated_locust_meta_class(  # type: ignore
        "The Locust class has been renamed to User in version 1.0. "
        "For more info see: https://docs.locust.io/en/latest/changelog.html#changelog-1-0"
    )
):
    pass


class DeprecatedHttpLocustClass(
    metaclass=deprecated_locust_meta_class(  # type: ignore
        "The HttpLocust class has been renamed to HttpUser in version 1.0. "
        "For more info see: https://docs.locust.io/en/latest/changelog.html#changelog-1-0"

View on GitHub (pinned to f391a716e1)

Solutions

Rename base class from Locust to User
Rename HttpLocust to HttpUser
Rename FastHttpLocust to FastHttpUser
Update imports to the new names from locust

Example fix

// before
from locust import HttpLocust, TaskSet
class MyLocust(HttpLocust):
    ...
// after
from locust import HttpUser, task, between
class MyUser(HttpUser):
    ...

Defensive patterns

Strategy: validation

Validate before calling

assert not issubclass(MyUser, tuple(b for b in MyUser.__mro__ if getattr(getattr(b, '__class__', None), '__name__', '') == 'MetaClass' or b.__name__ in ('Locust','HttpLocust','FastHttpLocust'))), "Use User/HttpUser instead of deprecated names"

Try / catch

try:
    class MyLocust(HttpLocust): ...
except ImportError as e:
    logging.error("Rename to HttpUser: %s", e)

Prevention

Use User/HttpUser/FastHttpUser in all new code
Run a 1.0+ migration check on old locustfiles

When it happens

Trigger: Subclassing locust.Locust, HttpLocust, or FastHttpLocust aliases from locust.util.deprecation (pre-1.0 names) after the 1.0 rename.

Common situations: Old locustfiles upgraded to Locust 1.0+ still using `class MyLocust(Locust)` or `HttpLocust`; tutorials predating the rename.

Related errors

AI-assisted analysis of locustio/locust@f391a716e1 (2026-08-29). Data as JSON: /api/errors/866c75b4461e2700. Report an issue: GitHub.