title: How can I run a Flask application
body: <p>The Flask official website says that we can run a Flask application by</p>
  
  <pre><code>$ export FLASK_APP=hello.py
  $ flask run
  </code></pre>
  
  <ol>
  <li><p>The second command doesn't work for me. </p>
  
  <pre><code>$ flask run    
  Command 'flask' not found, but can be installed with:  
  sudo apt install python3-flask
  </code></pre>
  
  <p>Instead this works </p>
  
  <pre><code>python3 -m flask run
  </code></pre>
  
  <p>How can I make the second command works? If I run <code>sudo apt install python3-flask</code>, will I get two installations of flask?</p></li>
  <li>Can the two commands be combined into one command without using environment variable?</li>
  </ol>