More Thread Tricks - Python

There is more to threads than just spawning them and sending them on their way. The threading module's Thread module contains a few more methods that you should be aware of. The first two deal with naming threads. The method setName sets a thread's name, and the method getName retrieves a thread's name:

import threading

class TestThread ( threading.Thread ):

   def run ( self ):

      print 'Hello, my name is', self.getName()

cazaril = TestThread()
cazaril.setName ( 'Cazaril' )
cazaril.start()

ista = TestThread()
ista.setName ( 'Ista' )
ista.start()

TestThread().start()

No suprises there. Also, as you can see, threads have names even if you don't specify them.

We can also check whether a thread is “alive” using the isAlive method. If the thread hasn't finished executing whatever is in its run method, then it's classified as being alive:

import threading
import time

class TestThread ( threading.Thread ):

   def run ( self ):

      print 'Patient: Doctor, am I going to die?'

class AnotherThread ( TestThread ):

   def run ( self ):

      TestThread.run( self )
      time.sleep ( 10 )

dying = TestThread()
dying.start()
if dying.isAlive():
   print 'Doctor: No.'
else:
   print 'Doctor: Next!'

living = AnotherThread()
living.start()
if living.isAlive():
   print 'Doctor: No.'
else:
   print 'Doctor: Next!'

The second thread remains alive because we force it to wait using the time module's sleep method.

If we want to make a thread wait for another thread to terminate itself, we can use the join method:

import threading
import time

class ThreadOne ( threading.Thread ):

   def run ( self ):

      print 'Thread', self.getName(), 'started.'
      time.sleep ( 5 )
      print 'Thread', self.getName(), 'ended.'

class ThreadTwo ( threading.Thread ):

   def run ( self ):

      print 'Thread', self.getName(), 'started.'
      thingOne.join()
      print 'Thread', self.getName(), 'ended.'

thingOne = ThreadOne()
thingOne.start()
thingTwo = ThreadTwo()
thingTwo.start()

We can use the setDaemon method, too. If a True value is passed with this method and all other threads have finished executing, the Python program will exit, leaving the thread by itself:

import threading
import time

class DaemonThread ( threading.Thread ):

   def run ( self ):

      self.setDaemon ( True )
      time.sleep ( 10 )

DaemonThread().start()
print 'Leaving.'

Python also contains a thread module that deals with lower level threading. The only feature I would like to point out is the start_new_thread function it contains. Using this, we can turn an ordinary function into a thread:

import thread

def thread( stuff ):
   print "I'm a real boy!"
   print stuff

thread.start_new_thread ( thread, ( 'Argument' ) )

Conclusion

There's much more to multi-threading than I explained in this article, but I will not bore you by extending the scope of this article to include everything. Moreover, as Guido van Rossum mentioned, the advantage gained by complex multi-threading in Python may be outweighed by the consequences. A small dose of common sense can eliminate much of the problems in simple multi-threading, however.

Threading is very important when dealing with computer applications, and, as I mentioned earlier, Python isn't excluded. When used properly, threads can be very beneficial and often even crucial, as I've outlined in this article.