<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def choose_boundary():
 """ Our embarrassingly-simple replacement for mimetools.choose_boundary. """

    boundary = binascii.hexlify(os.urandom(16))
    if six.PY3:
        boundary = boundary.decode('ascii')
    return boundary