If I define a class using the Thread and FTP moudles, 
start a process which gathers FTP responses, 
additional calls to the class may have the responses 
of the thread instead of the main loop (or vice versa)
  This causes weird and unexpected exceptions from the 
ftplib.

  For instance I get the following error when the 
thread process does a pwd() function
error_reply: 213 34603008  

  The "213" reply is a response from the main process 
size() function

---------
Code
---------
from time import sleep
from threading import Thread

class ftpMachine(Thread, ftplib.FTP):
    def __init__(self, svr, user, passwd):
        Thread.__init__(self)
        ftplib.FTP.__init__(self, svr, user, passwd)
        
    def run(self):
        for x in xrange(20):
            output="Thread -"+str(self.nlst())[:30]
            print output
            sleep (0.0100)

def main():
    aCon = ftpMachine("LocalFTP", "user", "")
    aCon.start()
    for x in xrange(20):
        output = "Main -- " + str(aCon.size("File"))
        print output  
        sleep (0.010)

Workround:
  Rewrite code to create a third worker thread for 
response isolation?  Don't know that this would solve 
the problem.


---------------
Exception example
---------------

Exception in thread Thread-1:
Traceback (most recent call last):
  File "C:\Python24\lib\threading.py", line 442, in 
__bootstrap
    self.run()
  File "dualFTPIssue.py", line 17, in run
    output  = "Thread output " + str(self.nlst())[:30]
+" ..."
  File "C:\Python24\lib\ftplib.py", line 448, in nlst
    self.retrlines(cmd, files.append)
  File "C:\Python24\lib\ftplib.py", line 396, in 
retrlines
    conn = self.transfercmd(cmd)
  File "C:\Python24\lib\ftplib.py", line 345, in 
transfercmd
    return self.ntransfercmd(cmd, rest)[0]
  File "C:\Python24\lib\ftplib.py", line 321, in 
ntransfercmd
    host, port = self.makepasv()
  File "C:\Python24\lib\ftplib.py", line 299, in 
makepasv
    host, port = parse227(self.sendcmd('PASV'))
  File "C:\Python24\lib\ftplib.py", line 566, in 
parse227
    raise error_reply, resp
error_reply: 213 34603008

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IMHO this isn't a bug, your accessing a shared resource (the FTP connection) 
from two threads without locking. Most of python's libraries aren't safe for this 
kind of use.

BTW. The fact that you subclass form thread and ftplib.FTP is immaterial, you 
will get the same effect if you create an ftplib.FTP and then use it in two threads.

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Unfortunately I can't start two instances of the FTP client 
as the separate instances use two conneciton resources.  I 
was hoping for a non-exception when a unexpsected response 
happens.  That would require re-working the module.
  For my workaround I set a time to determine when the 
transfer should complete instead of a querry.

  Thanks for your attention in this matter.

  Closing this bug as my case is an unusual one.

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I don't understand why you cannot use two connection resources. Are you 
running in a severely resource constrained environment?

Anyway, what you're doing right now is undefined behaviour. Unless explicitly 
stated otherwise classes in the stdlib aren't fully reentrant. You will therefore 
have to arrange some kind of exclusion mechanism. One way of doing that is 
to introduce a lock (probably wrapping the FTP client instead of using 
multiple inheritance in the progress). Another way it to introduce a 3th thread 
that performs the actual FTP operations and communicate with that using a 
queue. Please ask around on python-list/comp.lang.python if you need help 
with this.

BTW. I didn't close this bug, although I do understand why it was closed: the 
behaviour you describe isn't a bug but expected behaviour. 

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I am running on a unit that limits the FTP connections to 4 
high bandwidth connections and normally uses a passive FTP 
transfer.
  The response from the passive FTP transfer could come at 
any time.  Also, by inspection, the FTP module throws an 
exception when an unexpected reply happens.  So when I'm 
querrying the size of the clip on the destination and 
instead get a transfer complete message from the passive 
FTP session, that transfer complete message causes the 
exception.
  To "fix" this issue would requre that when the FTP 
message queue is read, that pending requests (passive 
transfers) would be considered before returning immediate 
command responses (cwd, ls, size, etc.).  If I get a couple 
of days, I may rewrite the functions that read the FTP 
responses and submit the changes for consideration.

  For my current project, I have decided not to querry the 
transfer to see if it completes, but instead to do a simple 
wait before sending the next transfer.