title: Possible to enforce type hints?
body: <p>Is there any advantage to using the 'type hint' notation in python?</p>
  <pre><code>import sys
  def parse(arg_line: int) -&gt; str:
      print (arg_line) # passing a string, returning None
  
  if __name__ == '__main__':
      parse(' '.join(sys.argv[1:]))
  </code></pre>
  <p>To me it seems like it complicates the syntax without providing any actual benefit (outside of perhaps <em>within</em> a development environment). Based on this:</p>
  <ul>
  <li>Are there any plans for python to contain <code>type</code> constraints within the language itself?</li>
  <li>What is the advantage of having a &quot;type hint&quot; ? Couldn't I just as easily throw that into the docstring or something?</li>
  </ul>
  <p>I also don't see this much in the python codebase itself as far as I can tell -- most types are enforced manually, for example: <a href="https://github.com/python/cpython/blob/3.7/Lib/argparse.py" rel="noreferrer"><code>argparse.py</code></a> and any other files I've glanced at in <a href="https://github.com/python/cpython/blob/3.7/Lib/" rel="noreferrer">https://github.com/python/cpython/blob/3.7/Lib/</a>.</p>