Global variable is not updated inside @get decorator

[CrazyGalEt]

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Example Code

import pika
import json

from fastapi import FastAPI
from aio_pika import connect
from aio_pika.abc import AbstractIncomingMessage
import asyncio

connection = pika.BlockingConnection(
    pika.ConnectionParameters('localhost'))
channel = connection.channel()

app = FastAPI()

data1 = {}

async def on_message(message: AbstractIncomingMessage) -> None:
  
        msg = json.loads(message.body)

        global data1

       data1 =  {
        'destination' : msg['destination'],
        'origin' : msg['origin'],
        'method' : msg['method'],
        'type' : msg['type'],
        'content' : msg['content']
        }
       
        print(data1)
  
@app.get("/{abc}/example")
async def example(abc: int):
   global data1
   return data1

async def main():
    
    connection_consumer = await connect("amqp://guest:guest@localhost/")
        
    async with connection_consumer:
        # Creating a channel
            channel = await connection_consumer.channel()
          
       
        # Declaring queue
        
            queue_4 = await channel.declare_queue("QUEUE4") 

        # Start listening the queue
          
            await queue_4.consume(on_message, no_ack=True)
 
            print(" [*] Waiting for messages. To exit press CTRL+C")
            await asyncio.Future()
    

if __name__ == '__main__':
      asyncio.run(main())

Another script to send messages to QUEUE4 

import pika
import json

connection = pika.BlockingConnection(
    pika.ConnectionParameters('localhost'))
channel = connection.channel()

channel.queue_declare(queue='QUEUE4')

def main():
   msg = {
        'destination' : 'string',
        'origin' : 'string',
        'method' : 'string',
        'type' : 'string',
        'content' : 'string'
        }
   channel.basic_publish(exchange='', routing_key='QUEUE4', body=json.dumps(msg))

if __name__ == "__main__":
    main()

Description

Receive a message (AbstractIncomingMessage) from a RabbitMQ Queue. Update data1 inside on_message and print it. The output is the expected.

Try to read this data by triggering the endpoint "/{abc}/example", the output is the empty dict.

I want it to output the msg received from the RabbitMQ Queue.

Operating System

Linux

Operating System Details

No response

FastAPI Version

0.1.0

Python Version

3.9

Additional Context

No response

[iudeen]

Not sure if this is a FastAPI issue.

[JarroVGIT]

Agreed with @iudeen , this code is not reproducible. Please provide a reproducible example so we can help you. Below is a working example using a global variable:

from fastapi import Body, FastAPI

app = FastAPI()

data1 = {}

@app.post("/update")
def update_data1(text1: str = Body(), text2: str = Body()):
    global data1
    data1["text1"] = text1
    data1["text2"] = text2
    return data1

@app.get("/get")
async def get_data1():
    global data1
    return data1

if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="0.0.0.0", port=8000)

Changing the global variable through a POST:

curl -X 'POST' \
  'http://0.0.0.0:8000/update' \
  -H 'accept: application/json' \
  -H 'Content-Type: application/json' \
  -d '{
  "text1": "this is text1",
  "text2": "this is text2"
}'

>>>
{
  "text1": "this is text1",
  "text2": "this is text2"
}

Getting the newly updated global variable through the GET endpoint:

curl -X 'GET' \
  'http://0.0.0.0:8000/get' \
  -H 'accept: application/json'

>>>
{
  "text1": "this is text1",
  "text2": "this is text2"
}

[CrazyGalEt]

Agreed with @iudeen , this code is not reproducible. Please provide a reproducible example so we can help you. Below is a working example using a global variable:

from fastapi import Body, FastAPI

app = FastAPI()

data1 = {}

@app.post("/update")
def update_data1(text1: str = Body(), text2: str = Body()):
    global data1
    data1["text1"] = text1
    data1["text2"] = text2
    return data1

@app.get("/get")
async def get_data1():
    global data1
    return data1

if __name__ == "__main__":
    import uvicorn
    uvicorn.run(app, host="0.0.0.0", port=8000)

Changing the global variable through a POST:

curl -X 'POST' \
  'http://0.0.0.0:8000/update' \
  -H 'accept: application/json' \
  -H 'Content-Type: application/json' \
  -d '{
  "text1": "this is text1",
  "text2": "this is text2"
}'

>>>
{
  "text1": "this is text1",
  "text2": "this is text2"
}

Getting the newly updated global variable through the GET endpoint:

curl -X 'GET' \
  'http://0.0.0.0:8000/get' \
  -H 'accept: application/json'

>>>
{
  "text1": "this is text1",
  "text2": "this is text2"
}

thanks for the reply, but that is not what im achieving to do.

[JarroVGIT]

You want to return a global variable in your endpoint, no? And this global variable is set from another function?

I am only demonstrating that this is perfectly possible, but you didn't provide a reproducible example, so I made my own.

[CrazyGalEt]

I have edited the code. To run the code you need to run a server rabbitmq.

[iudeen]

From your code, I don't see a line that starts FastAPI server. How are you starting it? If you're starting it outside like using uvicorn main:app it would not work the setup you have. You need to run both your consumer and server in same process.

[CrazyGalEt]

From your code, I don't see a line that starts FastAPI server. How are you starting it? If you're starting it outside like using uvicorn main:app it would not work the setup you have. You need to run both your consumer and server in same process.

Thanks for the hint. I solved my problem following the issue on this link https://github.com/tiangolo/fastapi/issues/543