What is the difference between asynchrony and parallel execution? What implements parallel execution in Python?

Asynchrony and parallel execution are different concepts.

• Asynchrony is a way of organizing code where operations that may take time (e.g., input/output) do not block the execution of the program. The code continues to run while waiting for the operation to complete. Asynchrony is often implemented through events, callbacks, promises, or async/await.

• Parallel execution is the simultaneous execution of multiple tasks or threads on different CPU cores. This is actual concurrent execution of code.

In Python, parallel execution is achieved using:

• The multiprocessing module — creates separate processes that can run in parallel on different cores.
• Multithreading modules (threading) — but due to GIL (Global Interpreter Lock), threads in standard CPython do not execute in parallel for CPU-intensive tasks, only for I/O operations.

Thus, parallel execution in Python is usually implemented through processes, while asynchrony is achieved through asyncio and similar libraries that allow efficient I/O operations without blocking.