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Python Condition notify() Method with Example
Python Condition.notify() Method: In this tutorial, we will learn about the notify() method of Condition class in Python with its usage, syntax, and examples.
By Hritika Rajput Last updated : April 25, 2023
Python Condition.notify() Method
The Condition.notify() is an inbuilt method of the Condition class of the threading module. The Condition class implements condition variable objects. A condition variable allows one or more threads to wait until they are notified by another thread. This method is used to wake any thread which is waiting on a condition variable. The thread must be called only when the lock has been acquired by the calling thread. This method can be used to wakes up at most n of the threads that are waiting for the condition variable; it is a no-op if no threads are waiting.
Read about Producer-Consumer here: Condition.acquire() Method
Module
The following module is required to use notify() method:
import threading
Class
The following class is required to use notify() method:
from threading import Condition
Syntax
The following is the syntax of notify() method:
notify(n=1)
Parameter(s)
The following are the parameter(s):
- n: It is an optional parameter, which specifies the number of threads that can waken up which were waiting on the condition variable. Its default value is 1.
Return Value
The return type of this method is <class 'NoneType'>. The method does not return anything. It notifies the threads that are waiting on the condition.
Example of Condition.notify() Method in Python
# Python program to explain the
# use of notify() method for Condition object
import threading
import time
import random
class subclass:
# Initialising the shared resources
def __init__(self):
self.x = []
# Add an item for the producer
def produce_item(self, x_item):
print("Producer adding an item to the list")
self.x.append(x_item)
# Consume an item for the consumer
def consume_item(self):
print("Consuming from the list")
consumed_item = self.x[0]
print("Consumed item: ", consumed_item)
self.x.remove(consumed_item)
def producer(subclass_obj, condition_obj):
# Selecting a random number from the 1 to 3
r = random.randint(1,3)
print("Random number selected was:", r)
# Creting r number of items by the producer
for i in range(1, r):
print("Producing an item, time it will take(seconds): " + str(i))
time.sleep(i)
print("Producer acquiring the lock")
condition_obj.acquire()
try:
# Produce an item
subclass_obj.produce_item(i)
# Notify that an item has been produced
condition_obj.notify()
finally:
# Releasing the lock after producing
condition_obj.release()
def consumer(subclass_obj, condition_obj):
condition_obj.acquire()
while True:
try:
# Consume the item
subclass_obj.consume_item()
except:
print("No item to consume, list empty")
print("Waiting for 10 seconds")
# wait with a maximum timeout of 10 sec
value = condition_obj.wait(10)
if value:
print("Item produced notified")
continue
else:
print("Waiting timeout")
break
# Releasig the lock after consuming
condition_obj.release()
if __name__=='__main__':
# Initialising a condition class object
condition_obj = threading.Condition()
# subclass object
subclass_obj = subclass()
# Producer thread
pro = threading.Thread(target=producer, args=(subclass_obj,condition_obj,))
pro.start()
# consumer thread
con = threading.Thread(target=consumer, args=(subclass_obj,condition_obj,))
con.start()
pro.join()
con.join()
print("Producer Consumer code executed")
Output
Random number selected was: 3
Producing an item, time it will take(seconds): 1
Consuming from the list
No item to consume, list empty
Waiting for 10 seconds
Producer acquiring the lock
Producer adding an item to the list
Item produced notified
Consuming from the list
Consumed item: 1
Consuming from the list
No item to consume, list empty
Waiting for 10 seconds
Producing an item, time it will take(seconds): 2
Producer acquiring the lock
Producer adding an item to the list
Item produced notified
Consuming from the list
Consumed item: 2
Consuming from the list
No item to consume, list empty
Waiting for 10 seconds
Waiting timeout
Producer Consumer code executed