Problem with Lock.aquire() and user defined exceptions

[djw]

Greetings,

I am having some difficulty with some _single_ threaded code that 
happens to contain thread locking around some data structure access. 
There is locking code beacuse I am going to have another thread access 
the data in the next rev of the code.

Red Hat Linux 9, Python 2.2.1


import thread

devices = None
device_lock = None

def getDevice(d):
     global devices, device_lock
     val = None
     print device_lock.locked() # prints 0
     device_lock.acquire() # hangs (blocks)
     try:
         val = devices[d]
     finally:
         device_lock.release()
     return val

def init():
     global devices, device_lock
     devices = {}
     device_lock = thread.allocate_lock()

init()
devices["foo"] = 1 # not the way the program really operates, but you 
get the idea
x = getDevice("foo") # prints 0, then hangs

This code is a bit of a contrived excerpt, but you get the idea. When I 
run this code in the framework of my larger program,  the program prints 
0 and then hangs on the acquire() call.

I might point out that this code is being called from a handler that is 
being called from asyncore, so there are several levels above this code 
(at least above getDevice()).

I am having a strangely similar, but different issue when I try to raise 
user defined exceptions in my code. If I define:

class DeviceError(Exception):
     pass

and then:

raise DeviceError

somewhere in my code, my program hangs, requiring a kill from the shell.

Is there some fundamental thing I am doing wrong here? This is the first 
time I have ever gotten such unexpected results from a Python program 
and I'm at a loss.

Thanks,

Don