Working with Tornado Futures

Working with Tornado Futures

Tornado is a Python web framework and asynchronous networking library. To understand Tornado futures, we first need to understand what a Future is. A Future is an object that is supposed to have a result in the future. In Tornado, Future is used as a placeholder for a computation that may not have completed yet.

Understanding Tornado Futures

A Future in Tornado represents a computed value that might not be available yet. Futures are often used when dealing with asynchronous operations. When you initiate such an operation, it returns a Future, which is a promise that the operation will eventually complete.

Think of it as ordering a pizza. When you place the order, you get a receipt (the Future). The pizza isn't ready yet, but the receipt is a promise that it will be.

from tornado import ioloop, gen

@gen.coroutine
def async_operation():
    # This is a stand-in for a more complex operation such as an HTTP request
    yield gen.sleep(1)
    return 'Result'

def handle_result(future):
    print(future.result())

future = async_operation()
future.add_done_callback(handle_result)

ioloop.IOLoop.current().start()

In this example, async_operation() is an asynchronous function that returns a Future. When the operation completes, handle_result() is called with the Future as an argument.

Using Tornado Futures

Here's a more detailed example on how to utilize Futures in Tornado.

from tornado.concurrent import Future
from tornado import gen, ioloop

def async_operation(future):
    print('Operation started')
    # Simulate long running operation
    ioloop.IOLoop.current().add_timeout(
        callback=lambda: future.set_result('Operation finished'), deadline=2)

@gen.coroutine
def main():
    future = Future()
    ioloop.IOLoop.current().add_callback(async_operation, future)
    result = yield future
    print(result)

ioloop.IOLoop.current().add_callback(main)
ioloop.IOLoop.current().start()

In this example, async_operation() is a function that simulates a long-running operation. It takes a Future as an argument and sets the result of the Future when it's done.

The main() function creates a Future and passes it to async_operation(). It then yields the Future and waits for it to complete. When the Future is done, the result is printed.

Exception Handling in Tornado Futures

Tornado Futures also provide a mechanism for dealing with exceptions in asynchronous code. If an exception is raised in a coroutine, it is stored in the Future and re-raised when the result is retrieved.

from tornado import ioloop, gen
from tornado.concurrent import Future

@gen.coroutine
def async_operation():
    raise Exception('Something went wrong')

def handle_result(future):
    try:
        print(future.result())
    except Exception as e:
        print(f'Caught exception: {e}')

future = async_operation()
future.add_done_callback(handle_result)

ioloop.IOLoop.current().start()

In this example, an exception is raised in async_operation(). This doesn't cause the program to crash immediately. Instead, the exception is caught when the result of the Future is retrieved in handle_result().

Tornado's use of Futures allows you to write asynchronous code that looks and behaves much like synchronous code, making it easier to write and understand. Remember that while Futures allow for more readable code, they also require careful exception handling to ensure your program behaves as expected.