Passing objects around an event queue in Python

Question

So i have a relatively convoluted setup for something I'm working on explained as follows: This is is python. and more of a rough outline, but it covers everything I need. Though the process next function is the same so feel free to clean that up if you want. ``` #timer event that runs every .1 second and processes events in a queue some_event_timer(): events.process_next() class Event_queue: def __init__(self): self.events = [] def push(self, event, parameters): self.events.insert(len(self.events), event, parameters) def process_next(self): event = self.pop(0) event[0](event[1]) class Foo: def __init__(self, start_value = 1): self.value = start_value def update_value(self, multiple): self.value *= multiple def return_bah(self) return self.value + 3 class Bar: def __init__(self, number1, number2): self.init = number1 self.add = number2 def print_alt_value(self, in_value): print in_value * (self.init + self.add) ``` That is a barebones of what I have, but it illustrates my problem: Doi…

Accepted Answer

Instead of passing in the function to call `func1` and the arguments that should be passed to the function, pass in a function `func2` that calls `func1` with the arguments that should be passed in.

```
d = {"a":1}
def p(val):
  print val

def func1():
  p(d["a"])

def call_it(func):
  func()

call_it(func1)
d["a"] = 111
call_it(func1)
```

Within `func1`, `d["a"]` is not evaluated until `func1` actually executes.

For your purposes, your queue would change to:

```
class EventQueue(object):
  def __init__(self):
    self.events = deque()
  def push(self, callable):
    self.events.append(callable)
  def process_next(self):
    self.events.popleft()()
```

`collections.deque` will be faster at popping from the front of the queue than a list.

And to use the `EventQueue`, you can use lambdas for quick anonymous function.

```
events2 = EventQueue()
foo1 = Foo(4)
bar1 = Bar(4, 2)

events2.push(lambda: foo1.update_value(1.5))
events2.push(lambda: bar1.print_alt_value(foo1.value))
events2.push(lambda: bar1.print_alt_value(foo1.return_bah()))

events2.process_next()
events2.process_next() # 36.0
events2.process_next() # 54.0
```

For Edit:

In this case you need to "capture" the value in a variable that is more tightly scoped than the loop. You can use a normal function and `partial()` to achieve this.

```
for name in names_list:
  def update(name):
    names_objs[name].update_value(2)
  events2.push(partial(update, name))
```

Passing objects around an event queue in Python

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