为什么我的python else语句不会触发？

Question

Here is the code, these are dummy classes that will eventually be replaced by something more useful. What I want the while loop to do is pull data from the queue to see if a poison pill was dropped. If not I want whatever is in the else statement to trigger. However for some reason it will wait till it gets a poison pill and only execute the kill condition if statement

class test_imports:#Test classes remove 

      def import_1(self, control_queue, thread_number):
          print ("Import_1 number %d started") % thread_number
          run = True
          count = 1
          while run == True:
                alive = control_queue.get()                
                count = count + 1
                if alive == 't1kill':#<==will trigger
                   print ("Killing thread type 1 number %d") % thread_number
                   run = False                   
                else:#<== won't trigger
                     print ("Thread type 1 number %d run count %d") % (thread_number, count) 

If needed the rest of the code is:

import multiprocessing 
import time 

class test_imports:#Test classes remove 

      def import_1(self, control_queue, thread_number):
          print ("Import_1 number %d started") % thread_number
          run = True
          count = 1
          while run == True:
                alive = control_queue.get()                
                count = count + 1
                if alive == 't1kill':
                   print ("Killing thread type 1 number %d") % thread_number
                   run = False                   
                else:
                    print ("Thread type 1 number %d run count %d") % (thread_number, count)     



      def import_2(self, control_queue, thread_number):
          print ("Import_2 number %d started") % thread_number
          run = True
          count = 1
          while run == True:
                alive = control_queue.get()                   
                count = count + 1
                if alive == 't2kill':
                   print ("Killing thread type 2 number %d") % thread_number
                   run = False
                else:
                     print ("Thread type 2 number %d run count %d") % (thread_number, count)


class worker_manager:
     def __init__(self):
        self.children = {}

     def generate(self, control_queue, threadName, runNum):
        i = test_imports()
        if threadName == 'one':
            print ("Starting import_1 number %d") % runNum
            p = multiprocessing.Process(target=i.import_1, args=(control_queue, runNum))
            self.children[threadName] = p
            p.start()        
        elif threadName == 'two': 
            print ("Starting import_2 number %d") % runNum
            p = multiprocessing.Process(target=i.import_2, args=(control_queue, runNum))
            self.children[threadName] = p
            p.start()
        elif threadName == 'three':    
            p = multiprocessing.Process(target=i.import_1, args=(control_queue, runNum))
            print ("Starting import_1 number %d") % runNum
            p2 = multiprocessing.Process(target=i.import_2, args=(control_queue, runNum))
            print ("Starting import_2 number %d") % runNum
            self.children[threadName] = p
            self.children[threadName] = p2
            p.start()
            p2.start()

        else:
            print ("Not a valid choice choose one two or three")     

     def terminate(self, threadName):
         self.children[threadName].join


if __name__ == '__main__':
    # Establish communication queues
    control = multiprocessing.Queue()
    manager = worker_manager()

    runNum = int(raw_input("Enter a number: ")) 
    threadNum = int(raw_input("Enter number of threads: "))
    threadName = raw_input("Enter number: ")
    thread_Count = 0

    print ("Starting threads") 

    for i in range(threadNum):
        manager.generate(control, threadName, i)
        thread_Count = thread_Count + 1              

    time.sleep(runNum)#let threads do their thing

    print ("Terminating threads")     

    for i in range(thread_Count):
        control.put("t1kill")
        control.put("t2kill")

    manager.terminate(threadName) 

Please note import_2 is identical to import_1 except prints something different. The point is to prove the ability to handle different thread types.

Answer 1

In your driver code, you control.put("t1kill") first.

And your handler for t1kill sets run = False , so you won't come back through the while run == True loop ever again.

So, there's no opportunity for your else to be triggered.

If you want to test it, just add that put s some dummy value:

for i in range(thread_Count):
    control.put("dummy")
    control.put("t1kill")
    control.put("t2kill")

However, in your real code, you're probably going to want that manager.generate method to put some useful values on the queue.

---

As a side note, you're making your code more complicated than it needs to be.

First, it's almost always a bad idea to write while run == True: instead of just while run: . As PEP 8's Programming Recommendations section says:

Don't compare boolean values to True or False using ==.

But really, you can just return as soon as you're done, and scrap the run flag entirely:

while True:
    alive = control_queue.get()                
    count = count + 1
    if alive == 't1kill':
        print ("Killing thread type 1 number %d") % thread_number
        return                   
    else:
        print ("Thread type 1 number %d run count %d") % (thread_number, count)

(There are some people who will tell you that break , early return , etc. are "bad structured programming". But Python isn't C.)