title: Why does starting a line with a comma and space in Jupyter generate a tuple of strings?
body: <p>I noticed today that in Jupyter notebook, writing <code>, = 4</code> produces the surprising output <code>('=', '4')</code>. (I was trying to see if comma could be used as a variable. Don't judge me.)</p>
  <p>After a few more tests, generally it seems that in Jupyter star a line with <code>&quot;, &quot;</code> will format whatever is left on the line into a whitespace-separated tuple of strings:</p>
  <pre><code>, def my_function():
  </code></pre>
  <p>produces</p>
  <pre><code>('def', 'my_function():')
  </code></pre>
  <p>and</p>
  <pre><code>, one_space: two_space:  five_space:     no_space:
  </code></pre>
  <p>produces</p>
  <pre><code>('one_space:', 'two_space:', 'five_space:', 'no_space:')
  </code></pre>
  <p>In Python cli this all just gives syntax errors, so this is apparently some kind of Jupyter magic command, but I haven't been able to figure out where this would be documented. Any help and references would be appreciated.</p>