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A Condition object in Python is a synchronization object that allows multiple threads to wait for a specific condition to be met. It is similar to a Lock, but it will enable you to synchronize threads not only on the acquisition of the lock, but also on the release of the lock.

To better understand this, consider the following example. In the Producer-Consumer problem, if one Producer produces an item and one Consumer consumes it, the Consumer cannot consume it until the Producer produces it. As a result, the Consumer must wait until the Produced produces an item. And it is the Producer’s responsibility to notify the Consumer when an item is ready for consumption after it has been successfully manufactured. And, if the Producer’s item is consumed by multiple Consumers, the Producer must notify all the Consumers about the new item produced. This is an excellent application for the condition object in Python multithreading.

Syntax:

condition = threading.Condition([lock])

where the condition object takes in an optional lock object as an argument. If we do not provide anything then it creates a default lock.

Condition class methods:

Here is a list of the most commonly used methods of the Condition class in Python:

• acquire([blocking]): Acquires the lock. If blocking is True, the thread will block until the lock is available. If blocking is False, the thread will return immediately with a value of False if the lock is not available.
• release(): Releases the lock.
• wait([timeout]): Releases the lock and waits for the condition to be met. If timeout is specified, the thread will wait at most timeout seconds before returning. This must only be called when the calling thread has acquired the lock.
• notify([n]): Notifies one or more threads waiting for the condition that the condition has been met. If n is specified, n threads will be notified. If n is not specified, only one thread will be notified.
• notify_all(): Notifies all threads waiting for the condition that the condition has been met.

It is important to use the acquire and release methods to properly acquire and release the lock, as well as the wait and notify methods to wait for the condition to be met and to notify other threads that the condition has been met.

Example:

import threading

# Create a condition object
condition = threading.Condition()

# A flag that indicates whether the condition has been met
flag = False

# A function that waits for the condition to be met
def wait_for_condition():
    # Acquire the lock
    condition.acquire()
    # Wait for the condition to be met
    condition.wait()
    # The condition has been met, so do something
    print("Condition met!")
    # Release the lock
    condition.release()

# A function that sets the flag and notifies the waiting thread
def set_flag():
    # Acquire the lock
    condition.acquire()
    # Set the flag
    flag = True
    # Notify the waiting thread
    condition.notify()
    # Release the lock
    condition.release()

# Create and start the threads
t1 = threading.Thread(target=wait_for_condition)
t2 = threading.Thread(target=set_flag)
t1.start()
t2.start()

In this example, the wait_for_condition function will wait until the set_flag function sets the flag and notifies the wait_for_condition function that the condition has been met.

It is important to use the acquire and release methods to properly acquire and release the lock, as well as the wait and notify methods to wait for the condition to be met and to notify other threads that the condition has been met.

Note: also read about Timer Objects in Python

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