title: Can't concat bytes to str
body: <p>This is proving to be a rough transition over to python. What is going on here?:</p>
  
  <pre><code>f = open( 'myfile', 'a+' )
  f.write('test string' + '\n')
  
  key = "pass:hello"
  plaintext = subprocess.check_output(['openssl', 'aes-128-cbc', '-d', '-in', test, '-base64', '-pass', key])
  print (plaintext)
  
  f.write (plaintext + '\n')
  f.close()
  </code></pre>
  
  <p>The output file looks like:</p>
  
  <p><code>test string</code></p>
  
  <p>and then I get this error:</p>
  
  <pre><code>b'decryption successful\n'
  Traceback (most recent call last):
    File ".../Project.py", line 36, in &lt;module&gt;
      f.write (plaintext + '\n')
  TypeError: can't concat bytes to str
  </code></pre>