Locust polymorphism with class as argument

Question

I'm writing Locust scripts and want to extend a base class. There are two values (dto_class and api_suffix) that are different from one sub-class to another. Everything else is shared

locust_base.py (base class):

### locust_base.py ###
from locust import HttpUser, between, task
## other imports ##

class BaseUser(HttpUser):
   """
   do some stuff        
   """
   def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.dto_class = kwargs.pop('dto_class')
        self.api_suffix: str = kwargs.pop('api_suffix')
        """
        set other stuff
        """

The sub-classes (e.g. locust_specific_dto.py) look like:

"""
locust_specific_dto.py
"""
from locust_base import BaseUser

class SpecificDtoUser(BaseUser):
   def __init__(self, *args, **kwargs):
         super(SpecificDtoUser, self).__init__(dto_class=SpecificDto, api_suffix="specificEndpoint", *args, **kwargs)

However, when running locust -f locust_specific_dto.py, this error gets output:

KeyError: 'dto_class'
2024-05-09T18:09:14Z <Greenlet at 0x21e4d99d580: <lambda>> failed with KeyError

[2024-05-09 14:09:14,811] WSAMZN-SPLR8QE1/CRITICAL/locust.runners: Unhandled exception in greenlet: <Greenlet at 0x21e4d99d580: <lambda>>
Traceback (most recent call last):
  File "src\\gevent\\greenlet.py", line 908, in gevent._gevent_cgreenlet.Greenlet.run
  File "{REDACTED}\AppData\Roaming\Python\Python311\site-packages\locust\runners.py", line 553, in <lambda>
    lambda: self._start(user_count, spawn_rate, wait=wait, user_classes=user_classes)
    ^^^^^^^^^^^^^^^^^
  File "{REDACTED}\AppData\Roaming\Python\Python311\site-packages\locust\runners.py", line 524, in _start
    self.spawn_users(user_classes_spawn_count, wait)
    ^^^^^^^^^^^^^^^^^
  File "{REDACTED}\AppData\Roaming\Python\Python311\site-packages\locust\runners.py", line 238, in spawn_users
    new_users += spawn(user_class, spawn_count)
    ^^^^^^^^^^^^^^^^^
  File "{REDACTED}\AppData\Roaming\Python\Python311\site-packages\locust\runners.py", line 227, in spawn
    new_user = self.user_classes_by_name[user_class](self.environment)
    ^^^^^^^^^^^^^^^^^
  File "{REDACTED}\Documents\dev\{REDACTED}\locust_base.py", line 23, in __init__
    self.dto_class = kwargs.pop('dto_class')
    ^^^^^^^^^^^^^^^^^
KeyError: 'dto_class'

Cyberwiz · Accepted Answer · 2024-05-09 20:46:59Z

0

Locust is trying to instantiate your BaseUser directly (not just your subclass). Set abstract=True on that class to skip it.

See https://docs.locust.io/en/stable/api.html?highlight=Abstract#locust.User.abstract

edited May 9, 2024 at 20:46

answered May 9, 2024 at 19:56

Cyberwiz

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3 Comments

FAESonata Over a year ago

reran with abstract=True at the first line of BaseUser, same error stackoverflow.com/a/64383314/24959674

Cyberwiz Over a year ago

Try using named parameters instead of kwargs and see if you get a better callstack. Are you on latest version of locust?

FAESonata Over a year ago

that worked (super().__init__(SubClass, "subClass", *args, **kwargs) in the SubClass) , thank you!

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