Check if a python thread threw an exception

By the time the join() call on a thread returns the thread's stack has been unwound and all information about exceptions has been lost. Thus, unfortunately, you'll need to provide your own mechanism for registering exceptions; some techniques are discussed here.

A simple technique for situations where you do not need to handle the exception is to use a global list and append to it pertinent information. Your code would become something like:

#!/usr/bin/python

from time import sleep
from threading import Thread, current_thread #needed to get thread name or whatever identifying info you need

threadErrors = [] #global list

def func(a):
    for i in range(0,5):
        print a
        sleep(1)

def func_ex():
    global threadErrors #if you intend to change a global variable from within a different scope it has to be declared
    try:
        sleep(2)
        raise Exception("Blah")
    except Exception, e:
        threadErrors.append([repr(e), current_thread.name]) #append a list of info
        raise #re-raise the exception or use sys.exit(1) to let the thread die and free resources 

x = [Thread(target=func, args=("T1",)), Thread(target=func, args=("T2",)), Thread(target=func_ex, args=())]

print "Starting"
for t in x:
    t.start()

print "Joining"
for t in x:
    t.join()

if len(threadErrors) > 0: #check if there are any errors 
    for e in threadErrors:
        print(threadErrors[e][0]+' occurred in thread: '+threadErrors[e][1])
        #do whatever with each error info
else: 
    #there are no errors so do normal clean-up stuff

#do clean-up that should happen in either case here

print "End"

Note: global variables are generally regarded as poor technique, but they are a simple mechanism for communicating between threads. You just have to remember that if one thread is sending info by this route the other thread has to be looking for it.