Python - Starting a Thread

In Python, starting a thread involves using thestart() method provided by the Thread class in thethreading module. This method initiates the thread's activity and automatically calls itsrun() method in a separate thread of execution. Meaning that, when you call start() on each thread object (for example., thread1, thread2, thread3) to initiate their execution.

Python to launch separate threads that concurrently execute the run() method defined in each Thread instance. And the main thread continues its execution after starting the child threads.

In this tutorial, you will see a detailed explanation and example of how to use the start() method effectively in multi-threaded programming to understand its behavior in multi-thread applications.

Starting a Thread in Python

Thestart() method is fundamental for beginning the execution of a thread. It sets up the thread's environment and schedules it to run. Importantly, it should only be called once per Thread object. If this method is called more than once on the same Thread object, it will raise a RuntimeError.

Here is the syntax for using the start() method on a Thread object −

threading.thread.start()

Example

let's see the below example, that demonstrates how to start a new thread in Python using thestart() method.

from threading import Threadfrom time import sleepdef my_function(arg):   for i in range(arg):      print("child Thread running", i)      sleep(0.5)thread = Thread(target = my_function, args = (10, ))thread.start()print("thread finished...exiting")

When the above code is executed, it produces the following result

child Thread running 0thread finished...exitingchild Thread running 1child Thread running 2child Thread running 3child Thread running 4child Thread running 5child Thread running 6child Thread running 7child Thread running 8child Thread running 9

Example

Here is another example demonstrating the working of thestart() method. You can observe that, by not calling the start() method on thread2, it remains inactive and does not begin execution.

import threadingimport timeclass MyThread(threading.Thread):   def __init__(self, threadID, name, counter):      threading.Thread.__init__(self)      self.threadID = threadID      self.name = name      self.counter = counter   def run(self):      print("Starting " + self.name)      print_time(self.name, self.counter)      print("Exiting " + self.name)def print_time(threadName, counter):   while counter:      time.sleep(1)      print("%s: %s" % (threadName, time.ctime(time.time())))      counter -= 1# Create new threadsthread1 = MyThread(1, "Thread-1", 1)thread2 = MyThread(2, "Thread-2", 2)thread3 = MyThread(3, "Thread-3", 3)# Start new Threadsthread1.start()thread3.start()print("Exiting Main Thread")

The above code will produce the following output −

Starting Thread-1Starting Thread-3Exiting Main ThreadThread-1: Mon Jun 24 18:24:59 2024Exiting Thread-1Thread-3: Mon Jun 24 18:24:59 2024Thread-3: Mon Jun 24 18:25:00 2024Thread-3: Mon Jun 24 18:25:01 2024Exiting Thread-3