how do i subclass threading.Event?

Question

In Python 2.7.5:

from threading import Event

class State(Event):
    def __init__(self, name):
        super(Event, self).__init__()
        self.name = name

    def __repr__(self):
        return self.name + ' / ' + self.is_set()

I get:

TypeError: Error when calling the metaclass bases
function() argument 1 must be code, not str

Why?

Everything I know about threading.Event I learned from: http://docs.python.org/2/library/threading.html?highlight=threading#event-objects

What does it mean when it says that threading.Event() is a factory function for the class threading.Event ??? (Uhh... just looks like plain old instanciation to me).

I just found http://stackoverflow.com/questions/100003/what-is-a-metaclass-in-python and am currently reading it. — Scruffy, Aug 01 '13 at 15:54

score 5 · Accepted Answer · answered Aug 01 '13 at 15:53

threading.Event is not a class, it's function in threading.py

def Event(*args, **kwargs):
    """A factory function that returns a new event.

    Events manage a flag that can be set to true with the set() method and reset
    to false with the clear() method. The wait() method blocks until the flag is
    true.

    """
    return _Event(*args, **kwargs)

Sinse this function returns _Event instance, you can subclass _Event (although it's never a good idea to import and use underscored names):

from threading import _Event

class State(_Event):
    def __init__(self, name):
        super(Event, self).__init__()
        self.name = name

    def __repr__(self):
        return self.name + ' / ' + self.is_set()

http://docs.python.org/2/library/threading.html?h says "class threading.Event". Kinda misleading. I guess I'll have to start getting used to opening up the actual python source files. I used to find that intimidating but I probably know enough Python now for it to be helpful. — Scruffy, Aug 01 '13 at 16:00

Bishop Arthur · Answer 2 · 2023-07-13T06:50:45.837

0

according to docs.python.org Changed in version 3.3: Event has been changed from a factory function to a class. so you can subclass Event and make your own Event instance.

edited Jul 13 '23 at 06:50

answered Jun 26 '23 at 06:52

Bishop Arthur

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1

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how do i subclass threading.Event?

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