What is the purpose of the Python Global Interpreter Lock (GIL)?

a) To prevent multiple native threads from executing Python bytecodes at once

b) To enable multiprocessing in Python

c) To optimize Python’s memory management

d) To allow Python code to run faster on multiple CPUs

Answer:

a) To prevent multiple native threads from executing Python bytecodes at once

Explanation:

The Python Global Interpreter Lock (GIL) is a mutex that protects access to Python objects, preventing multiple native threads from executing Python bytecodes simultaneously. The GIL ensures that only one thread can execute in the Python interpreter at a time, which simplifies memory management but can be a bottleneck in CPU-bound multithreaded programs.

While the GIL does not prevent Python programs from using multiple threads, it does mean that multithreaded programs often do not achieve true parallelism, especially in CPU-bound tasks. For I/O-bound tasks, however, the impact of the GIL is less significant.

import threading

def task():
    for _ in range(1000000):
        pass

threads = []
for i in range(2):
    thread = threading.Thread(target=task)
    threads.append(thread)
    thread.start()

for thread in threads:
    thread.join()

In this example, two threads are created and started, but due to the GIL, they will not run in parallel if the task is CPU-bound. The GIL can limit the performance gains from multithreading in such scenarios.

To achieve parallelism in Python, especially for CPU-bound tasks, the multiprocessing module can be used, as it bypasses the GIL by using separate processes instead of threads.