Threading: AssertionError: group argument must be None for now

Question

Here's an implementation of a stoppable thread and an attempt at using it:

import threading

class StoppableThread(threading.Thread):
    """Thread class with a stop() method. The thread itself has to check
    regularly for the stopped() condition."""
    def __init__(self, target, kwargs):
        super(StoppableThread, self).__init__(target, kwargs)
        self._stop_event = threading.Event()

    def stop(self):
        self._stop_event.set()

    def stopped(self):
        return self._stop_event.it_set()

def func(s):
    print(s)

t = StoppableThread(target = func, kwargs={"s":"Hi"})
t.start()

This code generates an error:

Traceback (most recent call last):
  File "test.py", line 19, in <module>
    t = StoppableThread(target = func)
  File "test.py", line 7, in __init__
    super(StoppableThread, self).__init__(target)
  File "/usr/local/Cellar/python3/3.6.2/Frameworks/Python.framework/Versions/3.6/lib/python3.6/threading.py", line 780, in __init__
    assert group is None, "group argument must be None for now"
AssertionError: group argument must be None for now

I would like to know why and how to fix it.

Answer 1

the first argument for thread is group, thus you need give name for target

super(StoppableThread, self).__init__(target=target, kwargs)

there is document

class threading.Thread(group=None, target=None, name=None, args=(), kwargs={})

https://docs.python.org/2/library/threading.html#threading.Thread

Answer 2

Try the following:

import threading

class StoppableThread(threading.Thread):
    """Thread class with a stop() method. The thread itself has to check
    regularly for the stopped() condition."""
    def __init__(self, *args, **kwargs):
        super(StoppableThread, self).__init__(*args, **kwargs)
        self._stop_event = Event()

The *args is a sequence with every positional argument and **kwargs is a dictionary with every key-wrod argument. By using this notation you are passing every argument that you pass to the StoppableThread constructor to its parent. The names of the vars *args and **kwargs are arbitrary.