Explain the concept of threads of execution in Python programming language.

In Python, a thread is a separate sequence of instructions that can run concurrently with other threads within the same process.

Features of threads in Python:

• Threads are created using the threading module.
• Due to the GIL (Global Interpreter Lock), only one thread executes Python code at a time in the standard CPython implementation, which limits parallelism in CPU-intensive tasks.
• Threads are useful for I/O-bound tasks, where the program can wait for a response and switch between threads.

Example of creating and starting a thread:

import threading

def worker():
    print("Thread is running")

thread = threading.Thread(target=worker)
thread.start()
thread.join()

Thus, threads in Python allow for concurrent execution of code, but for true parallelism in computations, processes (multiprocessing) are often used.