python threading timer on a class method

Question

I have a code block that I use for running a piece of code every 30 secs

def hello():
    print "hello, world"
    t = threading.Timer(30.0, hello)
    t.start()

The one below is a method of a class, which I really want to run every 30 secs, but I am having problems with it.

def continousUpdate(self, contractId):    
    print 'hello, world new'
    t = threading.Timer(30.0, self.continousUpdate, [self, contractId],{} )
    t.start()

When I run it, I get the following error

pydev debugger: starting
hello, world new
Exception in thread Thread-4:
Traceback (most recent call last):
  File "C:\Python27\lib\threading.py", line 552, in __bootstrap_inner
   self.run()
  File "C:\Python27\lib\threading.py", line 756, in run
   self.function(*self.args, **self.kwargs)
TypeError: continousUpdate() takes exactly 2 arguments (3 given)

I have also tried

def continousUpdate(self, contractId):    
    print 'hello, world new'
    t = threading.Timer(30.0, self.continousUpdate(contractId))
    t.start()

which somehow behaves as if it ignores the thread, and gives a recursion limit error

Solution

Try this:

t = threading.Timer(30.0, self.continousUpdate, [contractId],{} )

When you read self.continuousUpdate, the method is already bound to the object, even if you don't call it yet. You don't need to pass self again.

The reason the second version "ignores the thread" is that you call the method inside an argument to the Timer call, so it runs (and tries to call itself again) before the Timer ever gets started. That's why threading functions have you pass the function and its arguments separately (so it can call the function itself when it's ready).

Incidentally, you spelled "continuous" wrong.