Why is parallel task execution in multiple threads in Python impossible or limited?

In Python, parallel execution of tasks in multiple threads is limited due to the Global Interpreter Lock (GIL). GIL ensures that only one thread executes Python bytecode at a time, preventing memory issues but restricting parallelism.

Because of this, multithreading in Python is effective for I/O-bound tasks but not for CPU-intensive computations. For parallel processing of CPU tasks, the multiprocessing module is used, which launches multiple processes with separate interpreters.

Thus, GIL is the main reason for the limitations of parallel execution in Python threads.