title: flask - Server can't start
body: <p>I am using linux mint mate 17 (base on ubuntu 14.04), I installed flask by"</p>
  
  <pre><code>sudo apt-get install python-pip
  sudo pip install Flask
  </code></pre>
  
  <p>I have python2.7.3 as my default python.</p>
  
  <p>Then write the hello world program hello.py:</p>
  
  <pre><code>from flask import Flask
  app = Flask(__name__)
  
  @app.route('/')
  def hello_world():
      return 'Hello World!'
  
      if __name__ == '__main__':
      app.run()
  </code></pre>
  
  <p>And try to start the server by <code>python hello.py</code>, but it seems didn't start, and there is no any tip, and I can't access localhost:5000, any help?</p>