Explain what GIL is in Python and what role it plays in thread execution.

GIL (Global Interpreter Lock) — is a mechanism in the CPython interpreter that ensures only one thread executes Python bytecode at any given time. This means that multithreading in Python does not allow concurrent execution of Python code on multiple CPU cores, which limits parallelism in CPU-intensive tasks.

GIL is necessary to simplify memory management and prevent thread safety issues within the interpreter. However, for I/O-bound tasks or when using multiprocessing, this limitation is less critical.

Example: when using the threading module, multiple threads can run, but only one executes Python code at a time due to the GIL.