Python threading - How to repeatedly execute a function in a separate thread?

Question

I have this code:

import threading
def printit():
  print ("Hello, World!")
  threading.Timer(1.0, printit).start()
threading.Timer(1.0, printit).start()

I am trying to have "Hello, World!" printed every second, however when I run the code nothing happens, the process is just kept alive.

I have read posts where exactly this code worked for people.

I am very confused by how hard it is to set a proper interval in python, since I'm used to JavaScript. I feel like I'm missing something.

Help is appreciated.

Answer 1

I don't see any issue with your current approach. It is working for me me in both Python 2.7 and 3.4.5.

import threading

def printit():
    print ("Hello, World!")
    # threading.Timer(1.0, printit).start()
    #  ^ why you need this? However it works with it too

threading.Timer(1.0, printit).start()

which prints:

Hello, World!
Hello, World!

But I'll suggest to start the thread as:

thread = threading.Timer(1.0, printit)
thread.start()

So that you can stop the thread using:

thread.cancel()

Without having the object to Timer class, you will have to shut your interpreter in order to stop the thread.

---

Alternate Approach:

Personally I prefer to write a timer thread by extending Thread class as:

from threading import Thread, Event

class MyThread(Thread):
    def __init__(self, event):
        Thread.__init__(self)
        self.stopped = event

    def run(self):
        while not self.stopped.wait(0.5):
            print("Thread is running..")

Then start thread with object of Event class as:

my_event = Event()
thread = MyThread(my_event)
thread.start()

You'll start seeing the below output in the screen:

Thread is running..
Thread is running..
Thread is running..
Thread is running..

To stop the thread, execute:

my_event.set()

This provides more flexibility in modifying the changes for the future.