Python2 TypeError: must be unicode, not str for io module

I am using python netsnmp interface, in netsnmp, it is called C message and print error message, I want to write this message to string. So I found a blog: Redirecting all kinds of stdout in Python

But I have problems with Python 2.7.x, the code is for Python 3.x

this is a simple option:

#!/usr/bin/env python
# -*- coding: utf-8
from __future__ import unicode_literals

from contextlib import contextmanager
import io
import sys
import os
import tempfile

@contextmanager
def stdout_redirector(stream):
    original_stdout_fd = sys.stdout.fileno()

    def _redirect_stdout(to_fd):
        sys.stdout.close()
        os.dup2(to_fd, original_stdout_fd)

        #_buf = os.fdopen(original_stdout_fd, 'wb')
        _buf = io.open(original_stdout_fd, 'wb')   # for BufferWritter object, not file object

        sys.stdout = io.TextIOWrapper(_buf)

    saved_stdout_fd = os.dup(original_stdout_fd)
    try:
        tfile = tempfile.TemporaryFile(mode='w+b')
        _redirect_stdout(tfile.fileno())
        yield
        _redirect_stdout(saved_stdout_fd)
        tfile.flush()
        tfile.seek(0, io.SEEK_SET)
        stream.write(tfile.read())
    finally:
        tfile.close()
        os.close(saved_stdout_fd)

f = io.BytesIO()

with stdout_redirector(f):
    print('foobar')
    print(12)
print('Got stdout: "{0}"'.format(f.getvalue().decode('utf-8')))

      

        
        
        
      

    

but run this code:

Traceback (most recent call last):
  File "test2.py", line 40, in <module>
    print('foobar')
TypeError: must be unicode, not str

      

        
        
        
      

    

I have a search for several hours and cannot explain the reason