[FIXED] Queue.asyncio Python get element without remove it

Issue

In python code , Is there a way to check the last élément in the asyncio queue without remove it? i have to check element before get it.

i try to like a simple queue but it doesnt work print(self.main_queue[-1]) or print(self.main_queue._queue[-1]) or self.main_queue.__dict__['queue'][-1] i put data with

self.main_queue.put_nowait(new_json) 

I receive data from an exchange , do data_processing and then send the data to client. I want to check the data before the sending thanks for help

Solution

There is no way using the existing implementation, without trying to access its private members.

However, you can subclass it and add a method that will fetch the next element, and, on a subsequent get return that first, keeping the internal data as is.

One have to take some care so that other methods like empty still work, but it is feasible.

This should do:

class InspectableQueue(asyncio.Queue):
    _sentinel = object()
    _next = _sentinel
    async def get(self):
        if self._next is self._sentinel:
            return await super().get()
        value = self._next
        self._next = self._sentinel
        return value
    def get_nowait(self):
        if self._next is self._sentinel:
            return super().get_nowait()
        value = self._next
        self._next = self._sentinel
        return value
    def peek(self, default=_sentinel):
        if self._next is not self._sentinel:
            return self._next
        try:
            self._next = self._sentinel
            value = self._next = super().get_nowait()
        except asyncio.QueueEmpty:
            if default is self._sentinel:
                raise
            return default
        return value
    def empty(self):
        if self._next is not self._sentinel:
            return False
        return super().empty()
    def qsize(self):
        value = super.qsize()
        if self._next is not self._sentinel:
            value += 1
        return value

(just use the .peek() method in the above class to check next value withoug poping it)

Otherwise, if you don't mind depend on the current implementation of asyncio.Queue, knowing that it might change on any python version change (even minor updates), the internal data is kept in a ._queue attribute - which is a collections.deque instance- You can simple do:

if not self.main_queue.empty():
    next_value = self.main_queue._queue[0]

Answered By - jsbueno