Python3.6使用pexpect spawn触发TypeError问题求助

首先，明确你的核心场景与问题：你在CentOS 7系统的笔记本上，用Python 3.6.4编写Telnet自动化脚本时，遇到了TypeError: must be str, not bytes的错误，同时不确定自定义函数的语法是否符合Python 3规范。下面一步步帮你解决：

原脚本与错误信息 #

你的Telnet自动化脚本 #

#!/usr/local/lib python3.6
import pexpect
import sys
import re

def dologin(child):
    # Enter User Name
    child.expect ('login:')
    child.sendline ('admin')
    # Enter Password
    child.expect ('Password:')
    child.sendline ('123')
    return

def doprepcommands(child):
    # Enter config prompt
    child.expect ('NOS/27179080475072>')
    child.sendline ('config')
    # Issue command
    child.expect ('NOS/27179080475072/DEBUG/Config>')
    child.sendline ('show vlan')
    child.expect ('NOS/27179080475072/DEBUG/Config>')
    child.sendline ('exit')
    child.expect ('NOS/27179080475072/DEBUG>')
    child.sendline ('exit')
    child.expect ('NOS/27179080475072')
    child.sendline ('exit')
    return

# Spawn the telnet session
child = pexpect.spawn ('telnet 192.168.1.254')
# Display progress on screen
child.logfile = sys.stdout

dologin(child)
doprepcommands(child)

运行时的错误输出 #

================= RESTART: /home/aricent/Siva/test_debug.py =================
Traceback (most recent call last):
  File "/home/Siva/test_debug.py", line 37, in <module>
    dologin(child)
  File "/home/Siva/test_debug.py", line 8, in dologin
    child.expect ('login:')
  File "/usr/local/lib/python3.6/site-packages/pexpect/spawnbase.py", line 341, in expect
    timeout, searchwindowsize, async_)
  File "/usr/local/lib/python3.6/site-packages/pexpect/spawnbase.py", line 369, in expect_list
    return exp.expect_loop(timeout)
  File "/usr/local/lib/python3.6/site-packages/pexpect/expect.py", line 111, in expect_loop
    incoming = spawn.read_nonblocking(spawn.maxread, timeout)
  File "/usr/local/lib/python3.6/site-packages/pexpect/pty_spawn.py", line 485, in read_nonblocking
    return super(spawn, self).read_nonblocking(size)
  File "/usr/local/lib/python3.6/site-packages/pexpect/spawnbase.py", line 179, in read_nonblocking
    self._log(s, 'read')
  File "/usr/local/lib/python3.6/site-packages/pexpect/spawnbase.py", line 126, in _log
    self.logfile.write(s)
TypeError: must be str, not bytes

问题分析与修正 #

1. 核心错误：TypeError: must be str, not bytes #

在Python 3中，sys.stdout默认只能接收**字符串（str）类型的数据，但pexpect.spawn对象输出的是字节流（bytes）**类型，直接把sys.stdout赋值给child.logfile就会触发类型不匹配的错误。

解决方法很简单，改用sys.stdout.buffer（Python 3中专门处理字节流的标准输出对象）：

child.logfile = sys.stdout.buffer

2. 脚本中的其他潜在问题 #

• Shebang行错误：原脚本第一行#!/usr/local/lib python3.6是错误的，Python解释器通常位于/usr/local/bin/目录下，正确的Shebang应该是：

  #!/usr/local/bin/python3.6
  

  给脚本添加执行权限（chmod +x test_debug.py）后，就能直接运行了。

• 提示符中的HTML实体错误：原脚本里的NOS/27179080475072>是HTML转义后的>符号，实际设备提示符是>，所以要把所有>替换成>，否则pexpect.expect会匹配不到提示符，最终触发超时错误。

• 函数语法合规性：你的dologin和doprepcommands函数语法完全符合Python 3规范，函数定义、参数传递、return语句都没有问题，这点可以放心。

修正后的完整脚本 #

#!/usr/local/bin/python3.6
import pexpect
import sys
import re

def dologin(child):
    # Enter User Name
    child.expect('login:')
    child.sendline('admin')
    # Enter Password
    child.expect('Password:')
    child.sendline('123')
    return

def doprepcommands(child):
    # Enter config prompt
    child.expect('NOS/27179080475072>')
    child.sendline('config')
    # Issue command
    child.expect('NOS/27179080475072/DEBUG/Config>')
    child.sendline('show vlan')
    child.expect('NOS/27179080475072/DEBUG/Config>')
    child.sendline('exit')
    child.expect('NOS/27179080475072/DEBUG>')
    child.sendline('exit')
    child.expect('NOS/27179080475072')
    child.sendline('exit')
    return

# Spawn the telnet session
child = pexpect.spawn('telnet 192.168.1.254')
# Display progress on screen - 修正字节流输出问题
child.logfile = sys.stdout.buffer

dologin(child)
doprepcommands(child)

额外提示 #

如果后续遇到提示符匹配超时的问题，可以尝试：

• 给expect方法添加timeout参数，比如child.expect('login:', timeout=30)，延长等待时间；
• 用正则表达式匹配提示符，比如用child.expect(r'NOS/.*>')来匹配任意以NOS/开头、以>结尾的提示符，避免设备ID变化导致匹配失败。

内容的提问来源于stack exchange，提问作者Sivaprasath Kanakavel