Unregister Timers with parameters

Question

I am trying to use a timer for a function, but I need to provide it a parameter so I'm using the example from https://docs.blender.org/api/blender2.8/bpy.app.timers.html:

import bpy
import functools

def print_message(message):
    print("Message:", message)

bpy.app.timers.register(functools.partial(print_message, "Hello"), first_interval=2.0)

The problem is that I don't know how to unregister it. Trying with this:

if bpy.app.timers.is_registered(functools.partial(print_message, "World"):
    bpy.app.timers.unregister(functools.partial(print_message, "World")

Or this:

if bpy.app.timers.is_registered(print_message):
    bpy.app.timers.unregister(print_message)

Or even this:

   if bpy.app.timers.is_registered(functools):
        bpy.app.timers.unregister(functools)

And a lot of other things, but that doesn't work. Any idea? Thanks!

Answer 1

I am not an expert in Python, but if my knowledge from JavaScript translates well enough, then this is caused by the fact that the created function references are not equal. Let's say, you have a function called a:

def a(x, y):
    return x + y

It is stored as a reference, that can be assigned to multiple variables that will be equal to each other and itself as well:

print(a == a) # True
b = a
print(a == b) # True

But each time you call functools.partial, it creates a new function reference, which are then not equal to each other, not even if their parameters are the same:

c = functools.partial(a, 5)
d = functools.partial(a, 5)
print(c == d) # False

Or alternatively you can even directly compare the results.

print(functools.partial(a, 5) == functools.partial(a, 5)) # False

Because of this, if you want to later unregister a function created with functools.partial, you need to store a reference to it, so Python will be able to find which one to unregister by checking for equality among the registered ones, like for example this way:

e = functools.partial(print_message, "World")
bpy.app.timers.register(e, first_interval=2.0)

after which you can use the following code to unregister:

if bpy.app.timers.is_registered(e):
    bpy.app.timers.unregister(e)

because

print(e == e) # True