Question

I want to run a code that runs a function with a parameter (eg. greet(h)) every 5 seconds. I tried using threading but it doesn’t work. It executes just once. See the code below and the errors:

import threading

oh_hi = "Hi guys"

def greeting(hello):
    print "%s" % hello



threading.Timer(1, greeting(oh_hi)).start()

Error shown below:

> >>> ================================ RESTART
> ================================
> >>>  Hi guys
> >>> Exception in thread Thread-1: Traceback (most recent call last):  
> File "C:\Python27\lib\threading.py",
> line 530, in __bootstrap_inner
>     self.run()   File "C:\Python27\lib\threading.py", line
> 734, in run
>     self.function(*self.args, **self.kwargs) TypeError: 'NoneType' object is not callable

Kindly assist.

Thanks

Answer 1

As others have pointed out, the error is because you’re not passing the proper arguments to the threading.Timer() method. Correcting that will run your function, once, after 5 seconds. There are a number of ways to get it to repeat.

An object-oriented approach would be to derive a new threading.Thread subclass. While it would be possible to create one that does specifically what you want — namely print "%s" % hello — it’s only slightly more difficult to craft a more generic, parameterized, subclass that will call a function passed to it during its instantiation (just like threading.Timer()). This is illustrated below:

import threading
import time

class RepeatEvery(threading.Thread):
    def __init__(self, interval, func, *args, **kwargs):
        threading.Thread.__init__(self)
        self.interval = interval  # seconds between calls
        self.func = func          # function to call
        self.args = args          # optional positional argument(s) for call
        self.kwargs = kwargs      # optional keyword argument(s) for call
        self.runable = True
    def run(self):
        while self.runable:
            self.func(*self.args, **self.kwargs)
            time.sleep(self.interval)
    def stop(self):
        self.runable = False

def greeting(hello):
    print hello

thread = RepeatEvery(3, greeting, "Hi guys")
print "starting"
thread.start()
thread.join(21)  # allow thread to execute a while...
thread.stop()
print 'stopped'

Output:

# starting
# Hi guys
# Hi guys
# Hi guys
# Hi guys
# Hi guys
# Hi guys
# Hi guys
# stopped

Besides overriding the base threading.Thread class’s __init__() and run() methods, a stop() method was added to allow the thread to be terminated when desired. I also simplified the print "%s" % hello in your greeting() function to just print hello.