Locust: IndexError: Cannot choose from an empty sequence

[jawahar273]

Description of issue / feature request

  File "/media/jawahar/jon1/new_project/bm/testDev/lib/python3.6/site-packages/locust/core.py", line 268, in run
    self.schedule_task(self.get_next_task())
  File "/media/jawahar/jon1/new_project/bm/testDev/lib/python3.6/site-packages/locust/core.py", line 329, in get_next_task
    return random.choice(self.tasks)
  File "/media/jawahar/jon1/new_project/bm/testDev/lib/python3.6/random.py", line 258, in choice
    raise IndexError('Cannot choose from an empty sequence') from None
IndexError: Cannot choose from an empty sequence

Repeately i am getting this error after Start swarming number of users.

Expected behavior

No Error related to this.

Actual behavior

Traceback showed about

Environment settings (for bug reports)

• OS:Ubuntu 17
• Python version: 3.6.5
• Locust version: 0.8.0/0.8.1

Steps to reproduce (for bug reports)

Run some api and you will get this error

[cgoldberg]

IndexError: Cannot choose from an empty sequence

@jawahar273,
That exception gets raised when there are no tasks defined. Can you verify you actually declared some tasks in your locustfile? (either use the @tasks decorator or define a class that inherits from TaskSet)

for Locust devs,
A nice enhancement would be to catch the IndexError in /locust/core.py and raise a RuntimeError instead.. It should display an intuitive message like "No tasks defined in locustfile", and then exit.

[cgoldberg]

ah.. we should check for this in code.

[jawahar273]

import logging

from locust import TaskSet, task

logger = logging.getLogger(__name__)


class UserBehavior(TaskSet):

    def __init__(self, parent):
        super().__init__(parent=parent)

        self.token_key = "Token "

    def base_url(self):

        return "/api/"

    def packages_url(self):

        return self.base_url() + "package/"

    def user_details(self):

        return {"username": "demo", "password": "demobmmb"}

    def on_start(self):
        """ on_start is called
            when a Locust start before
            any task is scheduled
        """
        self.login()

    def login(self):
        # self.token_key = 'Token '
        logger.info("login user")
        response = self.client.post(
            self.base_url() + "rest-auth/login/", data=self.user_details()
        )
        self.token_key = self.token_key + response.text

        logger.debug("response from host" + str(response))
        print("Response status code:", response.status_code)
        print("Response content:", response.text)

    @task(1)
    def currency_details(self):
        currency = self.client.get(
            self.packages_url() + "currency/",
            headers={"authentication": self.token_key},
        )

        if currency.status_code >= 300:

            logger.debug("response from host for currency" + currency.text)

        else:

            logger.info("success in currency", currency.status_code)

This is the actual code.

[cgoldberg]

what are the items in "Addtion feedback" about?

[jawahar273]

Leave it.
Did you get the error that I was trying to show.

[cgoldberg]

Did you get the error that I was trying to show

no

[jawahar273]

Yes i got the error after removing the @task(1) and if you run the code with @task(1) there is no error in running the locust.

Is this a series issue or not.

[cgoldberg]

if you write an invalid locustfile and don't declare tasks, expect things to break. As I said previously, the error message could be improved.