Python: "'str' does not support the buffer interface" on subprocess.communicate (migrating to 3.x)

Question

 cmd_a = "a\n{0}\nt\n{0}\nda\nw\n".format(number)
 cmd_b = subprocess.Popen("fdisk %s" % file_name, shell=True,stdin=subprocess.PIPE)
 fdisk_cmd.communicate(cmd_a)

This code works with Python2.x but on Python3.x it gives me:

 File "bootimage.py", line 44, in do_install_file
|     fdisk_cmd.communicate(cmd_a)
|   File "/usr/lib/python3.4/subprocess.py", line 930, in communicate
|     self.stdin.write(input)
| TypeError: 'str' does not support the buffer interface

Answer 1

In python 3, subprocess streams are binary.

To write a string, just encode a binary, in your case ascii codec is OK:

fdisk_cmd.communicate(cmd_a.encode("ascii"))