Mastering concurrent.futures.wait in Python

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Understanding the Problem

Here’s a brief overview of the scenario:

Main goal: Block main process until child processes finish execution.

Initial error: TypeError stating "Future object is not iterable" when trying to wait for individual futures.

Follow-up error: Warning indicating "coroutine 'wait' was never awaited" when modifying the approach.

This situation may seem daunting, but with the right clarification, the solution becomes clear.

Breaking Down the Solution

Key Takeaways Before Implementing wait

Futures as Objects: A Future object represents an asynchronous execution which should be handled as a sequence rather than individually.

Redundancy in Expressions: Redundant parentheses in expressions, like those in while statements, should be avoided to improve code clarity.

Correct Usage of wait()

Correcting Your Approach

To resolve the issue, it's important to recognize that the wait() function expects a sequence (like a list) of futures to wait on, rather than a single future object. Hence, instead of calling:

[[See Video to Reveal this Text or Code Snippet]]

You should invoke:

[[See Video to Reveal this Text or Code Snippet]]

Where f is a list containing all the futures returned by the submit() calls. This fixes the error because now you are passing a sequence to wait().

Using the Context Manager

Moreover, it's important to note that when using with statements with ProcessPoolExecutor, the executor automatically waits for all tasks to complete before moving on. Thus, using wait() explicitly becomes unnecessary in this context unless you want to perform additional actions post-execution.

Sample Code Illustration

[[See Video to Reveal this Text or Code Snippet]]

Anticipated Output

When executing the sample above, the output will show concurrent executions by each child process, calculating factorials in parallel. The final lines will indicate that all tasks have been completed without any unnecessary delays caused by failed implementations of wait().

Conclusion