All 15 Concurrency (asyncio/threading/multiprocessing) questions
More in Concurrency (asyncio/threading/multiprocessing)
How do you create and run a basic thread using the threading module? What is the basic pattern for running an async function using asyncio.run()? How does the Global Interpreter Lock (GIL) affect CPU-bound versus I/O-bound multithreaded programs differently? How do you run multiple coroutines concurrently using asyncio.gather()? How do you protect shared mutable state from race conditions when using multiple threads, using threading.Lock? How does multiprocessing.Pool let you parallelize a CPU-bound function across multiple worker processes? What is a race condition, and how does it differ from a deadlock? How does asyncio's event loop schedule and switch between multiple coroutines, and what makes this cooperative rather than preemptive? How do you safely run a blocking, synchronous function from within an asyncio coroutine without freezing the event loop? How do you share data between processes using multiprocessing, given that separate processes don't share memory the way threads do?
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Python › Concurrency (asyncio/threading/multiprocessing)

What is the fundamental difference between concurrency and parallelism, and how does this map to Python's threading versus multiprocessing modules?

Beginner

Answer

Concurrency means multiple tasks make PROGRESS over overlapping time periods (not necessarily simultaneously); parallelism means tasks run LITERALLY AT THE SAME INSTANT on different CPU cores. Python's threading module provides concurrency (constrained by the GIL for CPU-bound work), while multiprocessing achieves TRUE parallelism by using separate OS processes, each with its own Python interpreter and GIL.
# threading: concurrent, but GIL-limited for CPU-bound work
import threading
threading.Thread(target=cpu_bound_task).start()

# multiprocessing: true parallelism, separate processes
import multiprocessing
multiprocessing.Process(target=cpu_bound_task).start()
Real-world example Choosing multiprocessing for a CPU-heavy image-processing batch job to actually utilize multiple CPU cores.

Common follow-ups: Why doesn't the GIL limitation apply to multiprocessing the same way it does to threading?

The Global Interpreter Lock (GIL)
All 15 Concurrency (asyncio/threading/multiprocessing) questions