expect in python3 is throwing error as "must be in str , not bytes"

Question

I am migrating my code to python 3.4.3. This code works fine in python 2.4.3. but here it throws error in python 3.4.3. should I use anything different from expect ? Here is my code snippet which gets the error:

   telconn=pexpect.spawn('telnet 10.24.12.83')
    telconn.logfile = sys.stdout
    login=telconn.expect([":","key to proceed.",">"])
    if login==0:
        telconn.send("user1" + "\r")
        telconn.expect(":")
        telconn.send("paswd1" + "\r\r\r\r\n\n\n")
        login1=telconn.expect([">","key to proceed."])
        if login1==0:
            print("nothing")
        elif login1==1:
            telconn.expect("key to proceed.")
            telconn.send ("\003")
            telconn.expect(">")
    if login==1:
        telconn.send ("\003")
        telconn.expect(">")
        print("ctlc")
    elif login==2:
        telconn.send("\n\r")
        telconn.expect(">")

The error what I get is :

Traceback (most recent call last):
  File "cleanup1.py", line 128, in <module>
    Connect()
  File "cleanup1.py", line 53, in Connect
    login=telconn.expect([":","key to proceed.",">"])
  File "/corp/global/install-dependent/python/3.4.3/lib/python3.4/site-packages/pexpect/spawnbase.py", line 315, in expect
    timeout, searchwindowsize, async)
  File "/corp/global/install-dependent/python/3.4.3/lib/python3.4/site-packages/pexpect/spawnbase.py", line 339, in expect_list
    return exp.expect_loop(timeout)
  File "/corp/global/install-dependent/python/3.4.3/lib/python3.4/site-packages/pexpect/expect.py", line 97, in expect_loop
    incoming = spawn.read_nonblocking(spawn.maxread, timeout)
  File "/corp/global/install-dependent/python/3.4.3/lib/python3.4/site-packages/pexpect/pty_spawn.py", line 455, in read_nonblocking
    return super(spawn, self).read_nonblocking(size)
  File "/corp/global/install-dependent/python/3.4.3/lib/python3.4/site-packages/pexpect/spawnbase.py", line 157, in read_nonblocking
    self._log(s, 'read')
  File "/corp/global/install-dependent/python/3.4.3/lib/python3.4/site-packages/pexpect/spawnbase.py", line 115, in _log
    self.logfile.write(s)
TypeError: must be str, not bytes

Answer 1

The accepted answer is correct in that you're currently trying to log bytes and not string. But at least as of pexpect version 4.6, you can provide the encoding argument to spawn. So use:

telconn=pexpect.spawn('telnet 10.24.12.83', encoding='utf-8')

Then all communication with the spawned terminal is automatically decoded using utf-8, and you'll be able to use telconn.logfile = sys.stdout.

Answer 2

pexpect wants to log bytes, not decoded strings. You can just let it do that:

telconn.logfile = sys.stdout.buffer

sys.stdout defaults to expecting strings. Internal buffer is happy with bytes.

Answer 3

As of this bug report you should use spawnu instead of spawn to write unicode instead of bytes. You might not have known that spawn uses binary logfiles, and spawnu uses unicode logfiles.