locustio/locust · error · LocustError

In order to use a with-block for requests, you must also pas

Error message

In order to use a with-block for requests, you must also pass catch_response=True

What it means

ResponseContextManager.__enter__ raises LocustError if the request was not made with catch_response=True, because only then is the response wrapped in a context manager that allows manual success/failure marking. Using a with-block without that flag would silently do nothing, so the library fails fast.

Source

Thrown at locust/contrib/fasthttp.py:721

    _manual_result = None
    _entered = False

    def __init__(self, response, request_event, request_meta, catch_response: bool):
        # copy data from response to this object (use update to avoid sharing
        # the dict reference, which creates a GC-reference cycle that Python 3.13+
        # can collect mid-request — see #3388)
        self.__dict__.update(response.__dict__)
        try:
            self._cached_content = response._cached_content
        except AttributeError:
            pass
        self._request_event = request_event
        self.request_meta = request_meta
        self._catch_response = catch_response

    def __enter__(self):
        if not self._catch_response:
            raise LocustError("In order to use a with-block for requests, you must also pass catch_response=True")
        self._entered = True
        return self

    def __exit__(self, exc, value, traceback):
        # if the user has already manually marked this response as failure or success
        # we ignore the default behaviour of letting the response code determine the outcome
        if self._manual_result is not None:
            if self._manual_result is True:
                self.request_meta["exception"] = None
                self._report_request()
            elif isinstance(self._manual_result, Exception):
                self.request_meta["exception"] = self._manual_result
                self._report_request()

            return exc is None

        if exc:
            if isinstance(value, ResponseError):

View on GitHub (pinned to f391a716e1)

Solutions

1. Add catch_response=True to the request call used in the with-block
2. Drop the with-block and use the plain response object if manual result marking is not needed

Example fix

// before
with self.client.get("/api/item") as response:
    if response.status_code != 200:
        response.failure("bad status")
// after
with self.client.get("/api/item", catch_response=True) as response:
    if response.status_code != 200:
        response.failure("bad status")

def with_response(session, method, *args, **kwargs):
    kwargs.setdefault("catch_response", True)
    return getattr(session, method)(*args, **kwargs)

When it happens

Trigger: Writing 'with self.client.get("/url") as response:' in a FastHttpUser task without catch_response=True in the request kwargs.

Common situations: Copy-pasting with-block response validation examples from Locust docs while omitting the catch_response=True argument, often after refactoring an existing plain request call.

Related errors

• If you want to change the state of the request, you must pas
• Tried to set status on a request that has not yet been made.
• In order to use a with-block for requests, you must also pas
• Tried to set status on a request that has not yet been made.
• If you want to change the state of the request using .succes

AI-assisted analysis of locustio/locust@f391a716e1 (2026-08-29). Data as JSON: /api/errors/483788f463b90e5e. Report an issue: GitHub.