R lock for synchronization mechanism

r_lock.py

import threading

num = 0
lock = Threading.Lock()

lock.acquire()
num += 1
lock.acquire() # This will block.
num += 2
lock.release()


# With RLock, that problem doesn't happen.
lock = Threading.RLock()

lock.acquire()
num += 3
lock.acquire() # This won't block.
num += 4
lock.release()
lock.release() # You need to call release once for each call to acquire.