title: Could not import "D": FLASK_APP
body: <pre><code>from flask import Flask
  app = Flask(__name__)
  
  @app.route('/')
  def hello_world():
      return 'Hello, World!'
  </code></pre>
  
  <p>I am new to Flask. I wrote this basic code and save it in hello.py in my D:\Cat_vs_Dog\scripts folder.</p>
  
  <p>Then in command prompt, I wrote the following commands.</p>
  
  <pre><code>C:\Users\Ketan Ingale&gt;set FLASK_APP=D:\Cat_vs_Dog\scripts\hello.py
  
  C:\Users\Ketan Ingale&gt;flask run
   * Serving Flask app "D:\Cat_vs_Dog\scripts\hello.py"
   * Environment: production
     WARNING: Do not use the development server in a production environment.
     Use a production WSGI server instead.
   * Debug mode: off
  Usage: flask run [OPTIONS]
  
  Error: Could not import "D".
  </code></pre>
  
  <p>I am getting this error. What should I do...?</p>