title: Writing "None" to a file in python
body: <p>I have a txt file that contains rows of JSON objects.
  I'm parsing this file in Python, and I'm writing a file that every row in it will be a record (Comma separated) I've built from the JSON object.</p>
  
  <p>Now, when I'm building this file - some of the values can be Null (or None in Python). So this is what I write:</p>
  
  <pre><code>a = 'abc'
  b = None
  str = a + "," + b
  file.write(str+\n)
  </code></pre>
  
  <p>But I keep getting this error: 
  <code>TypeError: coercing to Unicode: need string or buffer, NoneType found</code></p>
  
  <p>So my question is - How can I write "Null" values into the file, in a string, so when I load the file into the table - the value in that position will actually be Null?
  How can I keep this value in a file?</p>
  
  <p>Thank you!</p>